I need help diagnosing this problem!

When I drive my 2004 Z06 (3,500 miles) it makes a thunk sound. It only does this within the first minute of driving after the car has been sitting for at least an hour or two. Sometimes it is when I am backing out of my driveway, sometimes it is after I have already driven a few blocks. It has occurred in reverse and in first, second, and third gears. This has happened in the morning going to work and in the evening when I leave work. At first I thought it might be the brakes or clutch stuck down, but I have not been able to duplicate the problem or even relate it to when I use the brakes or clutch. Other than the thunk sound the car is driving great.
It used to be occassionally, but now it is almost every time I drive (after the car has been sitting for a while). The thunk is also getting lounder. I am worried that it might be unsafe or that it will damage the car, but since it is not yet happening every time, bringing it to the dealer is probably worthless (they won't be able to duplicate/find it).

Has anyone had a similar problem? Does anyone have any idea what this is? Since this only happens when I let the car sit for a while, I thought the solution might be to just drive the car continuously forever, but my boss told me that I have to come to work if I want to get paid; some people just don't understand Corvette owners!

 

Does the sound seem like it is coming from the rear? It may be the panel just behind the driver's seat. There have been some posts about this before but it has been a while. From what I recall it was the thin sheet-metal under the carpeting in the panel behind the seat leading up towards the reat hatch area.

I think some people were able to fix it by "pounding" on the panel to stretch the metal out a bit (don't beat up on your car because I said to though). Maybe some more folks will chime in.

In my case, it seems to happen mostly when I'm either turning or backing out of the drive-way (slight embankment that causes minor body flex). It only does it once and only after sitting for a while (adding to the belief that it is metal stretch/flex after sitting for a period of time). It doesn't appear to cause any problems or have any impact on drivability. Just a slight anoyance.

Hopefully others will chime in on this. Good luck.

 

The sound seems to be coming from the passenger side front of the car. It does not sound like metalic pop, although the carpet could make the sound duller. It sounds more like the sound of lightly hitting drywall with the side of your hand.
I have read the posts on the sheet metal behind the driver's seat flexing. I did not think that this was the source of the sound because it seems to be coming from the right front area and it is not what I would imagine that the flexing would sound like.
Similar to you, it only happens once after sitting. I too have a slight slope to my driveway. But it also happens at our flat parking lot at work. I may be mistaken about the area of the car that the sound is coming from, does anyone have an idea how to better determine the source area of the sound?

 

I am pretty sure it's the A/C compressor and related equipment. Normal stuff. Before you exit the car turn off the A/C and when you get in an hour later and start up see if the thunk has disappeared without the A/C turned on. Worth a try.

 

I have gotten this sound too. I can't figure out where it's coming from either, I always figured it was some small animal or a rock or some other debris I didn't see. Always startles me though.

 

It sounds like you had the problem I did. To confirm it drive at low speeds (>5mph) and then accelerate and then slow down again, repeat this cycle a few times without using the clutch at all. This cycle would bring about the clunk/thunk for me. This is my thread about my problem and solution:

http://forums.corvetteforum.com/showthread.php?t=862049

Please let us know how it goes.

Eugene

 

I had a similar sound coming from my 03 50th AE coupe. It started about a month after I got it home and sounded like it was coming from the rear passenger side. To me it sounded like a 'THUMP'. I mean I could hit the console of my S-10 PU with my fist and it would make the same sound.

I've had guesses from end-links to a cabin pressure relief value located in the one of the rear storage bins. You're right about the dealer, "Could Not Re-Produce the Sound. (What...? I'm making this Up?)

Anyway....mine would come and go, even used to think it was weather related and of course the daily driver excuse.

I't s now been about 2 months and I haven't heard it. So I'm hoping it's GONE!

Good Luck!

 

Here is an update:
I went to the dealer to ask advice. They told me that is is most likely something flexing and making the popping sound, but until it is easily reproduced, leaving it with them would be hit or miss. I did appreciate his honesty, rather than telling me to leave it and not find anything. I will wait until it is either all the time or it goes away.

BTW: A few people suggested driving with the A/C off to see if there was a problem with that. I drove with the A/C off and the problem remained, so I do not think that is the problem.

 

When I first bought my '04 vert, it did the same thing twice. It always occurred after a cold startup and either when backing up or driving off about a block. It too sounded like it was coming from the passenger side of the car. The vert now has 4100 miles on it and I haven't heard it since. I don't use the air-cond in the morning so it wasn't that either.