Howling from engine bay, varies with RPM, went away after sitting for a night. Thoughts?

First off, I am fully aware that diagnosing sounds over the internet is at best extremely difficult. Just looking for possibilities based on the situation to narrow down my diagnostics a bit. TL;DR it went away by the time I got to the shop so I'll have to try and force a replication somehow (if at all). So, this is a weird one. Drove the Cayman up about 120 miles to a family gathering this past weekend, tooled around country roads for a couple days, everything was hunky-dory. On the way home, right about at the halfway point of the journey I hit a moderate bump at highway speed (bad join from asphalt to a concrete bridge, no worse than anything else I'd gone over that trip, just enough to get a solid thump from the struts compressing) and something in the engine bay started howling. It continued to do this all the way home. No lights/codes/messages were thrown, engine otherwise sounded normal. The noise was too low in pitch to be belt squeal, sounded like a whirring / howling noise. Like a bearing starting to go south. It wasn't screaming loud, but enough to mask the regular engine noise a bit. When idling there was a pronounced tick audible in the cabin, and the howl got louder and angrier sounding as revs were applied. Got it home as gently as I could, parked it, called the shop and made an appointment to drop it off after work yesterday (drove my old car to and fro, the P-car sat parked all day). Got in to take it to the local Indie and all was normal. Drove all the way there (about 20 minutes / ~15 miles) with no issues, shop is unable to replicate as well. Before I start futzing with it do you folks have any thoughts? My first was that the water pump bearing was meeting an untimely demise, but one would think that wouldn't just go away overnight. On the other hand, I haven't seen the coolant temp needle move in any way other than expected, nor any indicators warning of coolant trouble (which seems a common thread for those failures once the bearing starts to go). The noise wasn't affected by turning the wheel, so power steering pump seems unlikely. The only straw I can grasp at right now beyond the WP bearing being JUST bad enough that the shock angered it temporarily, is that the oil indicator has been at the tippy tippy top of the range since I got the car 1500 miles ago. I would imagine on an ~80,000 mile engine that there would be at least some miniscule amount of consumption in that time (like half a bar on the display or something indicating a fraction of a quart burning up), or at least some difference in readings from the car not being quite level. I have no idea if the sending unit is able to tell if an overfill condition has been met, BUT if the engine oil is overfilled would it be possible for a shock at operating temp / pressure to overwhelm the AOS and would the ensuing flow of oil where oil should not go cause such a sound? I didn't see any smoke behind the car at the time, but it was dark and hard to tell.

My guess, and it's just a guess, is the water pump. When mine went it sounded like a 747 was landing behind my seat. Then it would stop. Then it became louder and more frequent over just a couple days. New water pump solved the problem. if you find my guess isn't the problem then I would follow the oil overfill issue. But, first thing you should do is get some of the oil out so that it reads where it should read. Too much oil can cause problems you surely want to avoid. Good luck.

You may have had something move/fall/bounce into the front of the engine where all the rotating stuff is. coulda been something left in the engine compartment that was jarred into falling into the drive belt or rotating equipment, or road flotsam/jetsam bouncing up. I wouldn’t think a water pump would make all those noises, then suddenly be quiet once it cooled down. You can take the front cover off and inspect the drive belt area as well as your water pump and idler pulleys for play, it’s a straight-forward job without much risk of bad things happening. Good luck.

Thanks, gents. I'm having the oil changed in the AM anyway since I'm unsure of when PO last did so (no sticker, of course), and when they drained a bit to inspect for the PPI they said it didn't look fresh. Not old and nasty or anything, just a little bit browned. Plus, you know, the whole possibly being overfilled by an unknown margin thing. We'll see how she does after that, and whether they notice anything funky when the bottom cover comes off. I had planned on pulling the top and front covers here in the next week or so anyway (barring a reappearance of The Noise necessitating fast action) to do some stuff like air filter, plugs, power steering fluid condition, and check the pulleys, so if they don't find anything else at the shop I can poke around in there a bit and see if I find anything of import. Still not ruling out a WP failing, as that's statistically likely at these miles assuming it's the original unit. It would be bizarre for the bearing to howl and whir like that then be fine the next day, though Budman's story sounds somewhat familiar.

I sort of recall hearing that a failing AOS can make some odd noises. No idea if it can be intermittent.

7 days; what's new ?

do check the wheel bearings and power steering lines as well.

Roger that on the PS lines. Definitely not a wheel bearing, as it varied with RPMs while stationary as well as while moving (though I could stand to check those out just as a general thing).

I had a bad bearing on my alternator in my 981 that made a horrible howling sound. It was very difficult to diagnose, and the tech first thought it was the water pump. Sound went away when the accessory belt was removed and the car started. There was a very slight bit of play, but never would have thought that was the problem. Here's a link to some audio of the problem.

"Howling from engine bay, varies with RPM, went away after sitting for a night. Thoughts?" My first thought was "When was the last time you saw your cat?"

LOL. Luckily we have dogs, neither of which is large, but couldn't possibly crawl in there without a good bit of assistance and maybe some oil to ease the process.

Just an update - car's back, no weird noise after running it out to 5k upshifts on the long way home. Sounds like it did the day I picked it up. On the bright side, they gave me the old oil filter insert and barring normal old-oil crud the thing looks clean as a whistle. Not even the slightest hint of metal flakes.And the oil level actually reads within the boundaries of the display from the sending unit (though still at the upper end of the range). Will keep an ear out going forward, but at least all indications seem to be that all is well.

Have you checked the power steering fluid? That would be my guess.

I still plan on pulling the engine cover(s) to check that as well as some other maintenance items this weekend, and to check for play in the pulleys.

Very much looks to be AOS related. PS fluid is good, pulleys feel good, belt looks good. Some oil residue at the joints in the intake tubing was my first sign. Unhooked the lines from the AOS into the main intake tube and oil was clearly visible, but worse on the driver's side, probably just due to the geometry of that particular line letting it pool in the bend right before the connection to the intake. Will order a replacement and set aside a day to tear the intake down and de-oil everything, clean the MAF, and replace the skanky looking air filter while I'm at it. Started it with the cover off and gave a good listen - nice and quiet up front, ticking along both sides which I think is just the injectors actuating (does not at all sound internal and is coming from the fuel-rail area on both sides), and some intake whoosh. Only real bad news I got was some jackass spilled something behind the oil filler door and it ate the paint along that whole corner. Brushed some primer on to keep it from rusting until I can it it properly repaired :/ Thankfully it's nice and dry up there so aside from looking ugly there's no real damage to the metal at least. EDIT: Dong some shopping - I'm not buying the El Cheapo Uro Parts separator, does anyone have experience with the Vaico unit RockAuto sells? Altermatively, I can just order the one from Suncoast but they don't explicitly mention the manufacturer on it.

I buy almost all of my parts from Pelican Parts . If you have questions about a part you can call them or ask on their forum. They are very into Porsche and BMW , and know their stuff. Sent from my SM-N950U using Tapatalk

Another +1 for Pelican . Have been using them for many years.

I would buy from fcpeuro lifetime replacement on every part. Yes that includes fluids/oil. Sent from my SM-G930V using Tapatalk

Thanks guys. The ******* in me defaults to RockAuto for parts @Bougie Thanks for the heads up on FCP. Hadn't seen them before, and that lifetime replacement policy looks absolutely ridiculous. I gave them a shot on this one, just based on the probability this won't be the last AOS I have to replace.

Just to cap this off, OEM AOS and Mahle air filter from FCP are installed. No more weird whining. The old AOS had been bad for a while just judging from the amount of residue I found outside the intake tubing around the clamps, but thankfully the oil coat inside the intake tract was pretty light. Took a couple hours to take it all apart, wipe the piping / MAF down and reassemble - I didn't pull the manifolds themselves, however. I did notice a bit more intake noise coming from the plenum when moderate throttle is applied (sounds like a bro-off valve on an old-school turbo), but couldn't isolate any sort of leak so I'm going to assume that's normal.

I don't recall; did you ever say which Cayman this was ? That intake sound doesn't seem normal to me; not with a stock setup anyway.

It's an 07, base car w/ 5 speed and no mods. The extra "whsshhh" I heard was coming from the cross-tube part of the intake plenum, very audible with the cover off the engine. With the engine idling, tapping the gas hard enough to quickly bring it to just under 2k was enough to bring it out. Slow roll-on doesn't seem to do it. Additionally, there's a slight noise after shutting the engine off like it's leaking down. None of this is audible with the cover on. I rechecked all intake connections as well as the vacuum lines underneath the plenum - all seems just fine. Engine seems to be running normally, with no codes / messages.