Any guesses on this noise?
 

Recently I am noticing this muffled noise coming from the engine area. It is present at idle but goes away as soon as I start to accelerate. Come to a stop sign and there it is again. It is sort like a low muffled rumble. When I get out to try and locate it, it is even more difficult to make out because of the engine noise - so you can really hear it better sitting in the car.

I know this is vague, but does anyone have any thoughts?

Oh, this is on the '95 by the way.

Is this your E300D or 240?


Edit: whoops, missed the last line. Sorry, I can't help ya much :(

I have an '83 240D and experienced noise similar to the one you describe. I found two of the three air filter housing mounts were bad. It's a quick check and a cheap fix if it turns out to be your problem. Peace.

It's the '95 300D. Thanks for the tip on the 240D though, I have heard of that one, but haven't investigated on mine yet. Soon though.

So, any thoughts on the 300D?

Check your motor mounts. Acceleration will cause the engine to rotate and lift (with bad mm's) at idle you could be setting low and having a rotating component rub against something. This is a symptom I get with my W126 - and could be similar to your 95

.02 worth

Hmmm, hadn't really thought of that one for this noise - I think I would be happy with that. Just bought new mounts for the 240D, but should probably change the ones on the 300D as well.

On that note, is there a way to check the mounts aside from visual inspection (if they look broken down and cracked it's time to go)? I'm just asking because when I was examining the 240D (pre-purchase) it was obvious the engine had a terrible vibration - so I suggested that the mounts were probably shot - to which the PO reply that another guy who came to look at it wonder the same thing but reached down and felt(?) them and decided they were not the culprit. I just thought - really? okay, i guess - not sure how that works, but then again, what do I know.

I have to examine my SDL mounts from underside as they "smash" when they go bad. Topside view doesn't work for me. Your sound and symptom is identical to the SDL when a mount fails (usually driver side). Idle - the pulley hits fan shroud slightly causing a slight rumble. Hit foot feed - add torque it lifts the engine up and all is well.

Thanks for the tip. I will check this out tonight and let you know what I find.

Well, I am still not sure about this one. Maybe it is the motor mounts. I tried to look them over this evening, but it was hard to get a good look - the rubber appears to be alright.

Are the left and right mounts designed differently on this model. They looked different - not sure if the drivers side is a little colapsed or if it is simply designed as such.

On a related note. I took a closer look at the mounts on my new 240D tonight - the driver's side completely obliterated. :eek: Looks to be nearly busted in half and there remnants of rubber laying about. This would certainly seem to explain why the engine sounds so terrible right now.

Maybe I should just change out the mounts on the 300D anyway, probably due for them.

Hey folks,

Haven't had any resolution to this yet - too busy. However, I did rule out the motor mounts by jacking up the engine while at idle and the noise did not disappear.

Now I am wondering if a failing water pump can make a low rumble sound like this - if the bearings are starting to go? The sound appears to be coming from the front of the engine. With the engine running, if I look down on the water pump pulley it almost seems to have a slight wobble to it. So, what do you think - could this noise becoming from the water pump. Does it make sense that it goes away on acceleration? Thanks.

I am sure there are as many causes for this as there are people responding but in my case it turned out to be a belt that was just starting to fail. I couldn't see anything bad on the belt but I was changing them anyway and when I did the sound went away so I looked over the old belts and one was just starting to crack.

Thanks Phil. I actually replaced the serpentine belt on this one ('95) about a year ago, so I doubt that is it - but a good thought.

I wonder if there is some way I can verify it is the water pump, without just replacing it to see.

Tank, take a look at my about me page and go to the albums link for the Dallas GTG in Mt Vernon. There's a picture in the album with a method for checking motor mounts. Basically, it shows how to use a #2 pencil to check for bad motor mounts.

Is there a way you could post a sound bite for us to listen to?

I haven't had to do it on my MB but with other cars you can tell if the water pump is going out by taking the belt off and then grabbing the pully on the pump and shaking, pushing, pulling etc and if you feel it moving then it's time for a new one. The shaft of the pump should not move around in the bearing.

Thanks. I will check it out. I am pretty it is not the motor mounts, but it never hurts to check again.