991.2 GT3 transmission noise
 

Hi all,

Just picked up my 991.2 GT3 (manual transmission) yesterday. Immediately noticed a thump/clunk type of sound coming from the rear of the car at times. After driving around a bit and trying to narrow down the cause, it seems to occur after engaging the clutch...maybe about half a second or a second after. It's definitely a metallic thump/clunk of some sort, and based on when it occurs I assume it's from the transmission. At first I thought it was possibly related to shifter linkage, but it occurs even if I haven't shifted (e.g., pulling away from a stop in first gear), and it's not timed with the shift, but after. It seems to be more likely to occur if I accelerate a little bit harder or if the clutch release is quicker (for instance on a downshift). Obviously sound is difficult to describe in words, but is similar to something like the sound you might gate from a floating brake disc bumping off a caliper or some of the sounds you might get from a LWF when you disengage the clutch. No issues whatsoever with the drivability of the car, the clutch isn't slipping at all, gear engagement is positive and firm. I talked to the dealer and they stated this was a common thing with 991 GT3s and was just an internal transmission noise, but had no further details on exactly what or why. I've searched the forum and the net and haven't seen much on it, which makes me wonder how common it is. Just wondering if anyone else has experienced this?

Thanks,
Collin

Dealer stated it was a common thing among GT3s? My follow up question would have been, oh so you've had a lot of manual .2 GT3s in for service already?

I agree it's probably nothing but that comment is pure get rid of the customer BS.

Sorry, I should have been clearer. He said it was a known thing with PDK as well, including 991.1s.

Could be. Timing of the sound would be right for that.
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Thanks,
Collin

Could it be the intake opening sound when you press the gas pedal after the shift? Try shifting by a no-lift shift, if the sound disappears, then its the normal intake opening sound when pressing the gas pedal.

Thanks for the thought. I will give it a shot but it doesn't sound like intake noise to me (of course, I could be wrong!), plus the "clunk" I'm hearing also occurs after engaging the clutch on a downshift well after the throttle blip. But definitely worth checking.

The other thing I'm getting from all of this is that whatever this noise is, it isn't common!

Thanks,
Collin

The clunk noise from the intake opening in the .2 manual is unlike any intake noise I have heard. Please keep us posted after you try the no-lift shift.

Sounds like it's slack in the drivetrain. Could be anything from out of spec. gear backlash to just the rear end getting loaded after being unloaded (when you disengage and reengage clutch). I had this type or rear end "clunk" in other cars with manual transmissions. The common variable was they all had mechanical rear LSD. I think one or two had Torsen differentials. Not sure what the mechanical diff. in the GT3 is. I did drive around in a new .2 GT3 with a MT for a few hours and I didn't notice any clunking noise though...

OK, managed to drive the car a bit more today and experiment a bit to see if I could figure out where this was coming from and why. I think I've actually got 2 separate but similar-sounding things going on. The first is just basic mechanical noise from the gearbox when shifting, and this lessens as the transmission heats up. I suspect I can hear it more in the GT3 (compared to my former GTS) because of the reduced insulation. It's nowhere near as noisy as a race car, and the sound characteristics are somewhat different, but that's where some of the noise is coming from. I don't believe it indicates there is a problem or issue, it sounds like normal mechanical noise. The second is as gago1101 said intake noise (and if I'm ever in southern Cal I owe you a drink!). Very easy to reproduce, just cruising along off-throttle in any gear and punch the gas (maybe 40%-50% throttle) and I very clearly hear a clunk type of sound from behind me. I would assume both PDK and MT cars would experience this since it's not transmission related. So I'm wondering if this is something others are hearing with 991.2 GT3s? If so great, if not I'll take it in and get it checked. On my car it is *very* noticeable and actually gets irritating at times. No-lift shift may be the way to go just to keep it from closing and reopening. Thanks!

There's a big difference between a "clunk" in the drivetrain (which is both audible and you can feel it) and the sound of the throttle body opening and sucking in air, which is perfectly normal (and I think it sounds pretty cool to be honest). Your description above made it seem like there was an actual clunk/thud coming from the rear end, rather than just the air intake lol. Have you never had any other high performance car? They all have that same sort of sound... (if that's really what you're hearing).

Is this the sound you're hearing?

Thanks for the response.

No, this isn't a normal intake sound...it's much more solid and metallic sounding. But it does only occur on somewhat heavy throttle, so I'm assuming it's intake related. And yes, I have/had quite a few high performance cars :). I'm going to try to drive/ride along in some other new GT3s and see if they sound the same. It'd be nice if I could actually get to the engine and directly see/hear what's going on, but that's not going to happen.

Can you record a video of the noise with your phone?

Yes, I will next time I'm in it.