mbkaiser

Hey guys, I just registered today although I've been reading this forum for ages. I've always just searched this forum and found the answer to my question until now.

This is driving me crazy. A few weeks ago we got a very intense rain storm. I was driving through a road, not flooded but it had about an inch of water on it and I was doing between 30-35 and I got a very loud, very intense feeling knocking coming from underneath the pedals. It varied with engine speed and if I let off the gas entirely the knocking would cease. If I maintained a constain speed, the knock would maintain a constant knock-per-minute.

No CEL, temp was normal. It stopped after 30 seconds or so and didn't come back. I did a brief look around and figured maybe something was stuck underneath the car and got free.

Then on Friday we got another rain storm and it happened again. Same exact situation. Intense rain, some water on the road, and about 45mph speed. Went away after a minute or so.

I've been under the car all day and I can't see anything that's loose. The exhaust is tight, the panels are all tight, the engine and tranny mounts only have 8,000 miles on them. New lower control arms. I checked for debris, I checked all of the suspension components...nothing is out of the ordinary. The car runs fine when it's dry, since the initial incident several weeks ago I've put at least 1,000 miles on the car and it's never ran better. It even runs fine when it's wet, aside from those few minutes every storm of knocking.

Is there something I could be missing? The knocking is definitely coming from somewhere around the underneath of the pedals, and I'm reasonably sure its coming from the directly right of the gas pedal (as you are facing the pedal). It is most definitely not pre-ignition or any other sort of engine noise, something is banging around.

Thanks in advance

Carsy

Thinking outside of the square :-

How are the brakes during these episodes? Is it the ABS coming into action?

Quenching of the hot exhaust & cats? Do you have the protective undercover fitted?

Thinking about it a little more , lots of water can make a loud noise under the car when the wheels force it inwards towards the floor pan. I have heard this noise when traveling through water at high speed.It is normal.

You see cars going through water spraying outwards copiously. Well, the equal amount of water goes inward under your floor pan at your feet. Physics I think !!

Slowing down is the answer.

namierequina

Hi, i am thinking if it is the same problem with my C200 2001. Although not in a wet condition.
For me, it seems like an activation of the brakes in an intermittent manner for about say around 3 or 5 seconds. At the same time i could see that the triangular alarm warning sign is flashing which will diminished as soon as the activation of the brake is gone.
So far, its not not coming again but i am so worried that it might cause an accident to me.
Hope i could get a help as well.

VVF

namierequina,
Sounds like ESP doing its job to prevent skidding...

Does it happen when you are cornering at speed?

namierequina

it happens once at a round about but i think i am at 50 or 60 kph. other than that it usually on a straight road after a sudden breaks. by the way, talking about that ESP i just continue to live with it as according to my friend this will not matter to me here in Middle east. so those problem when occurred im sure the ESP is already present in the error pages.

mbkaiser

It's definitely not traction control or anti-lock brakes, I know what both of those feel like.

If you were in the car, you wouldn't either (I mean that in a descriptive way, not a rude one). It's literally like something is physically banging against the floor pan and it perfectly coincides with engine speed, which has me thinking it was the exhaust or something. It doesn't vary with speed, it varies with rpms. If I'm doing 40 MPH at 4000 RPMs while accelerating, and it shifts to the next gear and is now at 2800 RPMs, the banging intensity will decrease (even though the speed is increasing).

However, my exhaust is tight. Extremely tight. I got under the car with it on a lift and I couldn't see anything. This is driving me nuts! What is the proper way of checking engine/transmission mounts? I'd hate to take it to the dealer and have them charge me $$$ just to say they can't find the issue either.

It has been over a week since the last thorough rain storm and no noise. Seems relegated to rain, but how? Very frustrating.

VVF

Could it be the heat shield above the prop-shaft then maybe?
May want to check there for looseness.
But then I'd think it would make noise all the time, not only in rain.