Whirring noise on acceleration

Hey gents, My 2001 996 TT is making a pronounced whirring/humming noise while under acceleration...a noise that seems to change (increase/decrease in pitch) depending upon RPM. It doesn't make any such noise at idle, nor does it seem to make any noise when pushing in the clutch (coasting at speed) and/or while revving the engine. Any idea's what this might be? Concerning. Thanks.

have you also tried asking in the TURBO forum? https://rennlist.com/forums/996-turbo-forum-61/

I seriously doubt this is an issue related to the TURBO'S but yeah, thanks, I'll try there as well.

My guess would be: a turbo a pulley a turbo feedback through the stereo or maybe a turbo (which is normal)

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He's suggesting you look in the forum devoted to turbos. This is the 996 na forum. Pull the fuse to the radio see if it still makes the sound. Is a high pitched noise kind of like radio static that increases decreases with throttle?

LOL, thanks...I've driven other turbo's and doesn't sound like a turbo noise to me. Stereo is off.

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Understand, thank you. I am thinking it was not related to the turbos, which is why I posted here. Thought the broader 996 audience might have experienced something similar. Kind of like that, yes...it changes in pitch depending upon rpm. Thank you.

pull the radio fuses D 8 & 9 to rule that out.

Awesome will try that. Thank you very much for the help here.

Transmission comes to mind. My mini cooper had a noise with similar symptoms and it was a bad bearing in the transmission. Hopefully I'm wrong.

I hope you are wrong too. As suggested, I will pull fuses for the stereo and try again. If the noise is still there, I fear bigger problems. Thanks for your input!

Usually when its static in the stereo you will hear it at standing still and just revving the engine. Also check your serp belt and pulleys. Take the belt off and try to wiggle all the pulleys for any play.

"It doesn't make any such noise at idle, nor does it seem to make any noise when pushing in the clutch (coasting at speed) and/or while revving the engine." ^This^ leads me to believe it's drivetrain related...

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Yes probably pinion bearing. The fuses were a quick way to rule out radio + amp.

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#1 rule of troubleshooting - always rule out the simplest/quickest stuff first, before moving on to more complicated tasks

Thanks guys...will be further troubleshooting this weekend and will report back. Thanks again. Appreciate the the help!

Ok, update...pulled the radio/speaker fuses and as expected, the sound is still there. A bit more clarification - seems the noise is non existent when driving around town. I only seem to hear it when I'm on the freeway (at speeds where I'm using 4th - 6th gears). Cruising along in 5th or 6th gear on the freeway, it seems to be the loudest between 2200 and 3000 rpm's. Again, every time I step on the gas ever so slightly (even when not in boost - so not a symptom of the Turbos). It's just a whirring, whining noise that changes in pitch linearly with RPM's.

Here are some videos where I tried to capture the noise. Pretty audible in these (poorly shot) videos. Thanks for your continued help/input! https://youtu.be/FS7ekCQ4s_I https://youtu.be/PvTqRaa3kF0 https://youtu.be/E3c8Y4TdHrA

It almost sounds like something is vibrating. Does it do it at higher rpms? Can you duplicate it in neutral while parked?

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Need to push it at higher RPM's and listen more carefully. The Kline 3" catless is sooo loud in the car (drone) it's hard to hear anything but exhaust at higher rpm's. No noises and can't be duplicated in neutral while parked. Thank you!

loose fastener (clip, nut/bolt)?? object in glovebox, cupholder, door pockets? object on floor/under or between seats? you have a sunroof? loose trim/window seals? best of luck.

Harmonic vibration excited by the loud exhaust. You can see it exciting the door pocket detritus in the first vid. Try things like stuffing the largest roll of paper towels, that fit, into the door pockets to see if that dampens the vibration. Could also be the speakers picking it up like drums resonating.

Well, it's official. My transmission is toast. How foolish it was to trust Zuluracerx and his "fresh" PPI from BBI. With an extremely loud kline 3" decat exhaust and the stereo, I didn't hear the transmission noises until after I bought the thing. The noises only became evident with no stereo and after a bit more time, while on the freeway. Couldn't hear it around town. Moral of the story? Don't trust anyone (no matter how well they check out and what they say) and get your own PPI done. (DUH) In the end, people who say they'll "stand by the car should you have any problems"...don't. Instead they accuse you of ruining the transmission by "launching the car", etc. Not the case. I cautiously drove the thing home in 6th gear, to and from the grocery store, to and from cars and coffee (in town) and to and from the Porsche shop to diagnose the noises. That's it. Anyhow, my fault for buying without getting it thoroughly checked. Anyhow, I'll be happy with the car once the transmission is rebuilt but damn, what a HUGE unexpected expense right out of the gate. Big lesson learned. Good thing my wife is taking it so well.

Rats! From what little I know about ours, I've heard these transmissions can be hard to diagnose. Sorry to hear that. Hopeful for a speedy recovery!

I doubt a good PPI would have turned it up anyway... sorry man. Sucks.

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Thanks man.... I tend to disagree though, a GOOD PPI should have found it... Had it up on the rack and you could hear the gearbox problems just by spinning the rear wheels manually. A more trained Porsche mechanic's ear should have noticed something while on the road and up on the rack. Was hard to hear with the loud exhaust while driving but I'm a Porsche newbie. Anyhow, thanks again.

Just trying to make you feel better.

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LOL, thanks...well, it kind-of worked.

Well think of it this way... you still have a 911 turbo. I'd donate a kidney for a 996 turbo... even with a bad transmission.

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Ha ha...yeah, well I'm going to have to sell one to pay for the repairs.

Here's the latest...input and suggestions welcomed! "My tech is just wrapping it up. I’ve heard the main components worn out are the pinion bearings, bearing retaining plate, 2nd gear, 1st/2nd shift sleeve, 3rd/4th fork – we’ll also recommend the synchros. Someone has been in this box before, 5th gear has been replaced with a stock 993 gear presumably BC the original was worn out. There are steel synchros in 3rd-5th gear positions also. Do you think you’ll want new steel ones again or brass ones for half the cost? Your ring and pinion has some uneven wear but is okay to reuse but not with TON of power. At a glance this will be much cheaper than buying our gearbox but it’s still going to be an expensive service. Estimate to follow."

That really sucks to have gotten duped with the bad transmission. Do the repair right the first time, though. Going with the steel synchros and the new ring and pinion will be worth the peace of mind. I don't know the numbers, but I'm sure that the cost for the new parts is less than having to pay the shop to break it open again.

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Sure does... Agreed and thank you for your input.

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Interested in the cost for the rebuild and parts. My tranny whine is on neutral / no throttle, which apparently is one of the bearings... I'm considering adding a rebuild to the project list.

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I'll send you the info when I get it...there are of course, a lot of options that can seriously jack up the price (brass vs steel synchro's, etc.). One can do things on the "cheap" (no real such thing for Porsche's), or spend a lot more depending upon what options you go for while you're in there.

Anyone have any thoughts about "while I'm in there"...doing the machining for the GT2 slave mod? Apparently the trans shop can do it for $250 (and now is the time to do that machine work as the trans has be apart so the bell housing to fit in their mill). I'd supposedly later have to drop the trans to change to the gt2 clutch release fork if I wanted to use the gt2 slave later. Worthwhile mod to do? Thanks.

Finally back on the road...trans is good. Glad to finally have it back. Also, I did make a mistake with the torque solutions trans mount. Lots of noise/chatter coming from the LWFW now. I know I was warned and told not to do it...but they already had it installed and told me to try it out. Oh well. Going back to the 997 OEM as soon as the car is ready for it's first trans fluid refresh.