rattling noise from engine
 

Hi,

I have noticed an odd noise coming from my 83 300D engine from time to time. Temperature does not seem to effect it, however, RPM does. I had a valve adjustment done, then drove the car to canada (~400 mi away), straight on the interstate. While up there it was nice so I had the windows down, and heard it for the first time. When passing through the 8-900 RPM range, through Id say apporoximately 1200, I hear this odd rattling noise, that sounds almost like when you shake a can of spraypaint. Almost as if there was a loose bolt rattling in my engine. However, I think it must be something else, as that would be a constant noise, and I think that this is something that vibrates at a critical frequency that is reached in that RPM range, then subsides at higher RPMs.
Any ideas what this may be?
Any help would be most appreciated.
Thanks

JMH

air filter mount - bracket
 

That is my guess. Check to see that all the rubber feet at there and that the bracket itself is not broken in half. Check carefully, because it may not be obvious.

Got the same noisy rattle at just over idle. Drove me nuts. Mine is from the Accessory Damper for the fan belt. Not sure if your model has this. PITA to change I guess. Happens quite often.

You can test it by pressing it tight towards the engine while at the same time increase the RPMs slightly. Watch your fingers for the fan.

JMH,

my car made a rattling at idle speeds and it was the side of the air cleaner hitting the valve cover. I pushed and pulled a little and it went away.

Nic

His model doesn't have the belt damper
 

602/03 have the damper, the old 617s don't.

I've heard belts make noises that would convince you that there was metal knocking.

There's also the possibility that your hearing the sound of early detonation. Air leaks in the fuel system perhaps? Make sure none of the little fuel return hoses at the injectors are wet. Or any of the fuel hoses for that matter.

Edited to add:
That air filter bracket you guys mention is almost always broken. So that's probably it.

I stopped having that problem when I replaced the engine dampers.

Hi,

OK, the noise is back. I dont always hear it, so it was tough to investigate besides shaking the air cleaner and just poking around. But tonight it wasnt even at a faster idle. I turned the car off, it sat for about 2 hours, then went back to it, slightly hot still, and turned it on. It started rattling immediately. I turned on the AC, and it got louder. I got out of the car, poped the hood and tried to investigate.
I found the following:

-opening the hood makes the noiser much harder to hear. It isnt from under the hood.

-from crawling around on the ground, it seems to be coming from the underside of the car, below the drivers seat. From the front of the car, there is the oil pan with drain bolt, then some stuff, then another oil pan, then this metal support that comes down slightly. It almost sounds like there must be a loose piece of metal on that support, or else a rock in my exhaust pipe that goes along right over there.

I was thinking maybe it was the fuel return line. My car has a cigar hose on it, but it is looking kind of bad. Plus, the car sometimes shakes at idle when hot. What kind of noise does the fuel return line sound like if it doesnt have the cigar hose attached? What side of the car would the noise come from?

Could a problem with the exhaust cause this? Are there any hangers that are supposed to support the exhaust pipe in that area? Maybe one rusted off of mine and so it rattles.

Any ideas would be most appreciated. Thanks

JMH

It sounds like the exhaust support. It bolts to the bellhousing and has a pipe clamp on it for the exhaust. It has probably just come loose or broken.

You need to get the car up in the air and bang around on the exhaust until you find it.