danmm7

Hi All,

2003 SL55. Car runs fine with no issues.

Ever since i bought the car, for the last month or so, i am hearing this random click / clunk like noise when the car is running and sitting in one spot (stop lights, parking spots).

It comes from under the car, and it sounds like it is towards the rear of the car. I don't think the noise is from under the hood. It is a random clunk noise too.....sometimes it happens every 2-3 seconds, sometimes i hear it once every 15-20 seconds. It is definitely NOT regular, timed noise.

Initially i thought it may be coming from the transmission but since it was happening when the car was at Park, and idling, i was not sure how it would make sense to be from the AT. The car is 100% stationary when the click / clunk can be heard.

Today, after a 15-20 mile long drive, i parked the car in the garage, turned the engine OFF, and i could still hear the click / clunk. Car was OFF....but the clunk noise was there, so it can't be transmission or engine related.

Could this be the ABC system clicking / clunking? Is it normal? Which component is making such noise?
Could this be exhaust related noise - caused by heat?

I made a video. Please turn on your sound, watch the video and let me know what this could be. This was recorded with the car completely OFF, after a drive.

mercy-me

Could be PSE vacuum pump in trunk. Open the lid and look to your left.

I had the same issue on my W220 where the pump would cycle over and over again even when parked. The motor finally gave out after about 5 years of constant running.

Bob

ian_uk1975

Hi, did you ever get to the bottom of this? Mine is doing exactly the same thing!

White Spyder

First make sure it is the PSE pump. Open the trunk and uncover it. It is located on the left side under the trunk floor. You will see some foam rubber that is gray. Remove it. The pump us under the hydraulic pump. Have someone start he car and then turn it off and close the doors. If you hear it cycle more than 4-5 times you more than likely have a leak. Check the trunk soft close, lumbar support in both seats and central locking systems.

Gurdeep Virdee

Hi did you ever get to the bottom of this?

danmm7

I did not find a 100% solid answer.... but i have some suspicions.
Likely it's from exhaust system... and a lot less likely from the ABC system.

Why not the ABC .... the clicking noise is not always present but if it's present when the car is running and i lower or raise the suspension - the clicks do NOT change at all. If this was ABC hydraulics related, i would assume that change in ride height will affect, even if temporarily, these mysterious clicks. Also, why would the clicks be there and be the same with engine on or off? Clearly, the ABC pump running or not, makes no difference.
I also did a pretty decent overhaul of my ABC system recently - new fluid, new filter, rebuilt both valve blocks, replaced some bad control valves, replaced all high pressure reservoirs with brand new units, and it made ZERO change in the clicks.

Why the exhaust.... well, one common thing i've noticed is, the car has to be warm for the clicks to happen. If it cools off - no clicks. If i just start the engine in the morning - no clicks. I need to drive it for some time, in order for the clicks to come back.

Again... i am not sure if i am on the right track, but after lots of observation and time under the car, i kind of learned to ignore these clicks. I don't even hear them so much anymore.

poppyboy

It’s clear to not be the ABC system. Did you rule out the PSE pump and/or pneumatic leak? Consider pulling the fuse to disable the PSE pump and see if the noise stops. Also, how many miles on the car? Just wondering if there may be an issue with the substrate within a catalytic converter and/or O2 sensor.

roman1999

did you ever find out the problem??? Thx!