Water causing loud vibration noise

[nickster]

The most bizzarre thing has started to happening! ONLY when water has been splashing up from the wheels do I hear a loud grrrrrrrrrrr noise from underneath the car (A4 Quat., B6). The sound resembles fan blades hitting something. The frequency of the sound increases as the engine is rev'd. After 10 or 15 seconds the sound disappears.

I have: 1) pushed the clutch in after hearing the sound and found that the sound changes (the grrrrr'ing sound) speeds up when I rev up the engine;
2) while up on the hoist my mechanic and I checked the obvious things like downpipe, tran. mount, shielding, subframe bolts. The belly pan is completely in tact. My mechanic is also baffled ..... and unlike most "sound related" problems that people encounter, the sound did occur this morning while he was in the car ..... and his words were "what the @#$@$@#$!"

Although we are still looking, as of this morning, we have no answers. Unfortunately I need the car all day so I can't leave it in the shop with them to troubleshoot.

What is so odd is that this sound never happens unless I drive through water fast enough to get some good spray off of the tires. The first time it happened I immediately shut off the engine thinking that I had blown something. No indicator lights indicated a problem, so I started it up again and the sound was gone!

And no, avoiding puddles is not a solution (ha, ha) ...... I live in Vancouver, BC where it never rains :)

Your thoughts would be great! Cheers,

Nick

[HeymyAudi]

Drive Shaft Rubbing on the Center Muffler... I had it on my exhaust when they first put it in... When the water hits the hot exhaust it actually causes it to contract and therefore having it rub on the driveshaft..

[dirtybrd]

Odd, but I do know what you mean about noises disappearing with others in the car. It happened to me all the time when I was a tech.

[nickster]

Drive Shaft Rubbing on the Center Muffler... I had it on my exhaust when they first put it in... When the water hits the hot exhaust it actually causes it to contract and therefore having it rub on the driveshaft..

Thanks for the reply ...... I will double check this, but I have a hard time believing that the pipe would move much as a result of expansion/contraction ... but hey, you never know.

[old guy]

Here ya go: Clicky click

[nickster]

Old Guy, I will have it up on a hoist again in the morning and we'll have a look. Fantastic help. I am amazed that the pipe can actually move that much. And yes, I was not looking forward to this troubleshooting fun! I don't think I mentioned that the last step taken yesterday was riding in the engine compartment while the car while being driven through some puddles ..... can you imagine the sight .... a 6'2" guy folded into the engine compartment rippin' down a narrow alley way in the pouring rain!

I will let you know what we find.

Cheers,

Nick

[nickster]

Old Guy, i hope that the system will let you know when a 'reply' involving your name is posted. I just wanted to say THANKYOU for the solution to this issue!

Cheers,

Nick