Jim Grant's Tech Tips
Bonneville, Rumbling/growling noise when wet
Q: I have a 92 Pontiac Bonneville.
When driving in rainy weather, if I run through any water, the vehicle
begins to make a terrible noise. You can feel it vibrate under your feet.
I thought this was the brake pads somehow vibrating because they got wet,
however the noise does not stop or change when the brakes are applied.
The pitch (if you will) will change when you place the transmission in
neutral and rev the engine. The car continues to run just fine, and eventually
the noise disappears. I have thought that water may be splashing up between
the converter and the heat shield and is percolating, but that would not
change with engine speed. I am at a loss. Any ideas?
forward exhaust on many vehicles is a dual walled pipe, one pipe inside
another. This pipe runs pretty hot and the sudden cooling by water will
cause the outer pipe to shrink more rapidly than the inner piper. Yup,
that would make for some strange noises.