CosmosC4S

I've been hearing this strange noise under the car, but it's only happened like 3 times in the last several months since I first heard it.

The noise sounds like it's somewhere right behind me and under the car. Seems to be in front of the engine area.
It doesn't sound like the engine, more like the transmission or driveshaft.
To describe it...Sounds like "a chain slipping off a sprocket"...or gears slipping?
Or like the sound when you accidentally shift into Reverse when you've moving forward, except it's not that harsh.
It lasts only a second, then it's gone and I'll never hear it again in a long time - weeks, or months before the next occurence.
Has always happened when I'm accelerating slow and gentle, like moving off from the lights.
Gives me the feeling that the car is moving in a higher gear than it's supposed to be, then as it downshifts, there's the split second grinding noise.
Or it could be the noise first, then the downshift...I can't be sure as I've not had the chance or enough time to really analyse it when it happened.

I tried to intentionally replicate the noise, by moving at higher gear, but it doesn't happen.
It also doesn't happen when I'm accelerating hard or downshifting aggressively.
Other than those few rare occurences, the transmission and everything else run very smooth.

Has anyone experienced this before? I'm thinking it could be early signs that I need a transmission service?
I sure hope it's not the transmission going bad...

It's a Tiptronic 2002 C4S @ 80600miles

Thanks.

VGM911

I think you ran over a raccoon.

greenjt

Trunk Monkey?

spiderv6

Whoaaaaa....doing that even once is not going to help!!

Tippy

Cosmos - Does this ever happen in reverse? My car makes a sound that I believe is similar to yours but it does it mostly in reverse or if the car downshifts to first abruptly. When I reverse, I hear two pops along with shaking of the car, I believe it is diff related. I am going to inspect this weekend and see if I can see something obviuous like an axle joint or loose bolts on the suspension. I will get back with my diagnosis, I am scared it is my diff!

eurotrashed

It could be the trunk monkey, although the tactical ones are usually mounted on top of the vehicle.

CosmosC4S

No, Tippy. I've never had it in reverse, only in those rare instances as described.
I think I'll consult my mechanic and also schedule a transmission service,
have been wanting to do that in a while.

Tippy

The more I read your description the more I believe it is the same in my car, the only difference is mine is usually on quick throttle burst in first gear when there is slack in the driveline. If I footbrake (hold the brake and give slight gas), the driveline will not "pop" or grind then.

99firehawk

tranny mount

CosmosC4S

Hmm..maybe mine's the early stage of a similar problem like yours...?
But I don't have any "popping" sound on mne though.
And like I said, when I push or drag the gears, it's smooth.

CosmosC4S

99firehawk, are you familiar with complaints like mine?

Do you mean a loose mount? Or worn parts?

Porsche_Smile

Does it sounds like MEEEEEEEEOOOOOOOWWWWWWWWWW...ouch? cause mine does.........

99firehawk

yes sir
get the car in the air and pull of the plastic panels
use a pry bar to move the mount
if you see tears in the rubber its time for a new mount
pretty common complaint and 80k miles is about the right time for one to wear out

CosmosC4S

Thank you very much, 99firehawk!
I'll have that checked out when I bring it in for a transmission service.