metal 'clunk' at 2500 rpm
 

When I have been slowing down and the engine revs have fallen to about 2500 rpm in my 997 C4S tip and I accelerate, a pretty loud metallic 'clunk' sound comes from the rear of the car. I would usually be in 2nd gear (as I tend to drive the car in manual mode) but it happens in any gear. I used to hear a simliar sound in a 996 6-speed manual which I drove for 3 months and I have heard a similar sound from other 997s driving past. Sorry if this is a dumb question but do others hear this sound and is it normal? Is it something to do with the transmission? Thanks

Sam

No such sound from my sixspeed Sam. Hopefully nothing major.

I know it's been 4 1/2 years since this thread started (and ended the same day), but I have exactly the same situation with my 2006 C2S. Any resolution? Thanks.

Got enough trans fluid? trans been serviced a the prescribed times? I don't know the the PDK trans well but it sounds like the trans slowly clunking into the next lower gear.

I have a similar issue to this that I've posted about a few times but have never gotten much information on it.

It's very subtle, if you don't know what to listen for you might not hear it at all (though once in a while it's a bit louder).

I have a 2006 manual , this doesn't have anything to do with shifting gears.

I found a thread on the 996 forum of a guy who described a similar thing :

https://rennlist.com/forums/996-foru...-welcomed.html

Here's a copy of what I posted there :

I'm trying to narrow down exactly what could be causing it. Some more information :

1. It's a "clunk" or a bit of dull clang; it sounds like it's coming from the drivetrain somewhere. It only happens when you get on the throttle gently around 2k RPM, it'll clunk and then the RPM picks up. Once you are up in higher RPM you can feather the throttle all you want and it won't clunk.

2. It seems to happen mostly if you are coasting (eg. giving no throttle and the car is slowly deccelerating) and then get on the throttle lightly, thus reversing the flow of torque through the driveline. Might happen more when coasting up hill, but can't say that for sure.

3. Happens mainly in 2nd or 3rd. I think it's easier to repro in 3rd. Probably happens in all gears, these are just the easiest ones to coast at 2k RPM.

4. It almost never happens when the car is cold, and it's much louder once the car is well warmed up after a few hours of spirited driving. Seems to indicate something about the lube getting warm.

5. Never clunks going over bumps or turning, only on throttle application, so I don't think it's any kind of loose piece clanging. Also had the motor mounts inspected so that's probably not it either.

There are a few things that are odd about it : there's no clunk when coming to a stop or when starting from a stop; those would be standard hallmarks for driveline lash. There's no clunk when changing gears, that would be a classic symptom of a DMF failure.

My best guesses are something in the AWD or the DMF. It's when the driveline is loaded in reverse (coasting up a hill) and then you get on the throttle, but only at 2-3k RPM, not higher, which is weird. Maybe it's a specific resonance.

I'm sure I could ignore it and the car would be fine, but it's driving me a bit batty. I'll see if I can get an audio recording.
cbzzoom is offline Reply With Quote

I bet it's pinging/knocking. I have noticed this too. Usually when you give sudden pressure to throttle. I bet everyone here is using 91 gas?

Really hard to diagnose clunks from pings, rattles and knocks w/o hearing it but you may be onto the answer here. Can't believe I posted on the OT almost 5 years ago. I had 2 OEM knees then ;)

Best I can tell from your post is what you are hearing is the clunk from drivetrain play. All the bearings/gears have some play and as the drivetrain loading switches from being under load from say a coast down on engine compression to being loaded from engine acceleration the system can clunk.

This drivetrain clunk is normal though some vehicles have more of and some have less. Generally the best thing is to try to drive the car in such a way to avoid the conditions that bring it about, though this is not a hardship based on my experience. Both my Porsches and many of my other cars have had this though none real bad.

Sincerely,

Macster.

Yeah, that's real similar and also occurs, but I believe is slightly different. Someone recently pointed out to me that the ping only occurs when you open up from slight throttle to bigger throttle, not when you go from no throttle to open throttle.

cbzzoom, I think we're both hearing the same thing. The "clunk" I hear occurs under exactly the same circumstances as you have described. The sound is subtle, yet definitely present. I do think it's easier to appreciate when you're the one doing the accelerating (as opposed to riding in the passenger seat). I know mine isn't related to AWD, since I have RWD. I also know it's not tip or PDK related because I have a manual. As was mentioned, it can likely be driven and will be fine, but it's frustrating not knowing.

Mine (a tip) has been doing this for several years. It occurs at low speed when some gas is applied. It sounds like it's coming from the drivetrain and not the engine. Since the car runs just fine I have always assumed that it is a benign quirk of the car.

My best guess is that Macster is right and it's just some driveline slack.

Unfortunately driveline slack is one of those problems that's almost impossible to track down. You have to go through all the components from the wheels through the CV's and U joints, half shafts, R&P, transmission gears, flywheel, etc. and even if you do that, it might not be any one component that's bad, but just a sum of a tiny bit too much play in each that adds up.

Oh well, no biggie...

Sometimes the car is just so perfect that I get overly obsessive about every little flaw. Even the slightest defect that I wouldn't normally notice in any other car I start worrying about. It's good to drive a rental car once in a while to get a reminder of all the clunks and grinding and understeer and mushy throttles that plague other machines!

My 2009 S edmits that sort of sound ( a low clunk) every so often. Strange. It usually happens when I hit the gas hard and the revs are low and the gear (stick) is too high. Always on the freeway and yes, I picked the wrong gear. I have never been to the dealer about this but will mention it and take a drive with a tech before the warranty expires.

Just throwing this out there but sounds like a motor mount to me.