tapping noise when gassing

[ryhi]

usually in the mornings when im gassing it i hear this tapping noise coming from the rear drivers side.. i have no clue what it is but it bugs me a lot. when im at a stop it makes a different sound...

[stox]

Let your mother in law out from under the hood. ;->

[jswong888]

I have similar noise and when I open the windows, it sounds like a rattle noise coming from under the car (right beneath the arm rest area). I suspecting it's my catalytic converter? (also, my CEL is also on). perhaps something inside the cat is busted and also casuing the O2 sensor to cause bad reading? any advice or help?

[jnolte]

Originally posted by jswong888
I have similar noise and when I open the windows, it sounds like a rattle noise coming from under the car (right beneath the arm rest area). I suspecting it's my catalytic converter? (also, my CEL is also on). perhaps something inside the cat is busted and also casuing the O2 sensor to cause bad reading? any advice or help?

do you smell rotten eggs?(the smell of a bad cat)

Go to rear of car and have someone rev the engine, do you hear a rattle?

hit the cat with a rubber mallet, hear any loose shit?

[Cschilderink]

Could be a motor or some sort of device that moves when you hit the gas. It could just be that its old and makes noise.

When I turn on/off my heat the motor to close the vent makes noise every time. Its just something that happens when cars get old.

[ryhi]

im pretty sure its not the cat. when i try to rev it in neutral it doesnt make the sound anymore.. it sounds like its coming from somewhere around the rear wheel??

[1998K]

Originally posted by ryhi
im pretty sure its not the cat. when i try to rev it in neutral it doesnt make the sound anymore.. it sounds like its coming from somewhere around the rear wheel??

FYI I've a rattle that can be heard only if I accelerate in neutral above but with VEHICLE RUNNING (about 80Km/h), it came at abt. 4000rpm.

The fact is that being stationary, the rpm limitation stop engine before rattling came out.

MB technician said me it's internal of the catalityc converter! Hoping that it will last.

Hope this be usefull info for you.

Hi:)

[mr. gatsbury]

I have a very slight rattle in the middle of the gears when I give it a healthy amout of gas or punch it... Not really sure how that helps you but when I get it checked out I will let you know...

[ryhi]

what i hear is a tapping/knocking noise. it isnt a rattle.. anyone have any other ideas?

[Kswiss]

what kind of sound does it make when the car is stopped.

[CKlasse]

Originally posted by ryhi
what i hear is a tapping/knocking noise. it isnt a rattle.. anyone have any other ideas?

Most likely it is the catalytic converter. Despite of what the MB claims, most MB cats last only 120K-150K miles. MLs' are the worst as they usually go bad at around 80-100k miles.

The Cat will make knocking/rattling noise when the engine is under load. You will notice power lost and MPG decrease as it gets worse. Once the catalyst started to broken apart into smaller pieces, they could go into the exhaust, thus ruining it.

Then finally your CEL will light up(for 1995 or newer cars). Sometimes, if the catalysts turn side way in the chamber, the CEL will light up right away.

Instead of guessing, have it diagnosed by the pro. Once you know exactly what's going on, then, only then, start shopping around.

Good Luck. ;)

[RivoA]

Just refreshing the "story", if anyone else has this problem. I used to have it and i couldn't find the problem until I had it replaced, it is ofc, a Tension Pulley making that sound.
If you're on neutral - nothing, but once you start driving you will start to hear it a bit before gear change, it's mostly happening when shifting from 1st to 2nd.