987.2 Cayman Engine whine

I am experiencing an engine whine from what appears to be the rear drivers side. As the car is driven, you can notice it becoming more pronounced the longer you drive. But what is really baffling to me is that its very loud once the car is turned off. Video captures the whine while its running and when the car is turned off. Any thoughts... 987.2 Engine Whine

Wow - that's an odd noise. If it was accessory drive/serpentine belt related it would stop when the engine stops turning. Since I'm assuming it's a US car - the engine compartment cooling fan is located on the passengers side, and that's where it's most noisy. And if the car is being driven the engine compartment fan should never turn on (it's for stationary engine running, or stationary engine shut off - and engine compartment heating up - you'll hear it turn on sometimes 10 minutes after shutdown as the residual engine heat pushes the engine compartment temperature up. I think you may want to remove the top engine compartment cover and try narrowing it down that way. It's a case where a mechanic's stethoscope would be a useful tool ($2.99 at Harbor Freight - good deal..) When you have a chance - please visit New Member Introductions and introduce yourself and your car..

What comes to mind is escaping pressurized air. As the pressure bleeds off, the frequency of the resonance drops. Baffling. Is this noise the same every time you kill the engine?

Thank you both for the very quick responses. My car is a weekend car and sometimes it goes longer that than that unfortunately. Life... When I get it out to charge the battery and do a quick run around town I do not notice the noise. When we are enjoying the car as we should be, I can notice the noise when I am in narrow road ways such as a parking lot or alley as it reverberates from the surroundings. The whine is constant and not overly concerning. However when I put her back in the stable and shut her down this is what I get. No dash lights, no codes just the sound in the video. I didn't really realize there was a fan in the engine compartment until deilberger 🔝 mentioned it to me as I was assuming they were all up front. AOS separator failing? No smoke on cold start up however...

The AOS isn't capable of such a noise, your noise has a speed related component, is sounds like a possible slowing rotational whine sound. The fact it is omnipresent is actually an advantage IMO, you should be able to drill down on it easier that way. As Don suggested the fan is a good start point but your car sounds a little like the Batmobile being shut off so I'm not sure it's Mr. Fan either.

I'd guess it is something pressurized. That could include power steering, coolant, A/C, and various vacuum connections. As mentioned, remove the engine cover. Also you might need to get under the car so you might need to raise the car on jack stands. You might also need to remove the firewall cover behind the seats. A mechanics stethoscope should narrow the source down to eliminate or pinpoint possibilities. Some thoughts: The PS pump and AC compressor are on the left (US driver's) side. Although the water pump is on the passenger side, there are water lines on both sides. There are various vacuum lines all over the place. Check all the fluid levels and the water & oil filler caps.

I'm guessing the AOS. That sounds like engine vacuum leaking down through a torn membrane. This is the way.

Gubi may have the call here, that should be easy to confirm if you have it apart and you have an extra body. You can be near the AOS when the car is cycled on and off and based on the video it should be apparent if you're right on top of it.

Thank you for the responses. In regards to the AOS, would that be temperature dependent on the heat of the engine. This sound only happens when I have taken the car for an extended drive. During short around town runs I do not experience it.

Mongo dunno. If I'm right about it being vacuum that's the first thing that comes to mind but there are other possibilities as well. Brake booster runs off vacuum, I think that's the vacuum pump in the lower left front of the engine? If that or the check valve is leaking that could do it. (Actually that's another thing to check, I guess. After you turn the car off, do the brakes still have boost for 1-2 stops?) Anyway, get the car hot, take off the top engine cover, and see if you can tell where it's coming from. A mechanic's stethoscope is cheap and will help a bunch. If it's happening all the time it'll be easier, obviously. Otherwise you'll probably need to get a buddy to start/stop the car while you listen.

So boristhespyder states that the AOS is not capable of such a noise yet you indicate that it could possibly be the AOS and he gives you a thumbs up is confusing to to me. I believe it's the AOC after pushing this to "reliable" outside sources. My intention is to replace the AOC and see where I go from there. Probably should be replaced anyways....

DJBL, do you have the PSE option? it also uses vacuum from the engine and the valve/actuator is near where the clip is taken....

Thank you for your response, but no I do not have that option.

Gubi, the AOS appears to be the issue. Replaced and no more Bat Mobile noises. Original AOS was removed and replaced and I took the old AOS apart to see if the membrane had failed, it had not. Either is was not making good seal or something else was going on with it. There are a couple of vids on YouTube explaining the procedure and they both indicated that you just give that thing a little push back and forth and it pops right out. Not in my case, it was an hours long project involving the wife and a screwdriver. When it did finally did come out the o rings were dry as a bone. My two cents.

Glad you sorted it out! The 987.2 AOS seems to be less problematic than the earlier ones, but I'm sure the rubber eventually wears out. Maybe it just wasn't making a good seal or something.