M20 rattle issue!
 

hey,

I have manual 89' 325i M20 with 249000.

Ive been hearing a rattle. It happens at about 2000 and 3000 rpm ( sometimes half way at about 2500). Its very similar to the e46 ZHP rattle if you have ever heard that before. Very mechanical sound, like marbles rattling in a jar. It will happen accelerating or decelerating, but only at those rpm. I tried revving the car up in neutral, and the noise is not there. Its only when the car is driving and under load .Not sure if its an engine issue or a tranny issue. At first it sounded like the engine but now I'm not sure. it only rattles for a short spurt and once past those rpm its gone. I tried reseaching the issue on other forums and such but didn't come up with anything. Its annoying. the engine works fine other than that, no problems i can see hear or feel. It seems to be coming from the mid to front section but hard to know fully since you have to be driving. its for sure not the rear of the car. Its seems like a bearing rattling maybe.

Any help would be very appreciated!
Thank

why does a clutch come to mind.

What part of the clutch? The guy who owned it before had the transmission seals done and they inspected the clutch and said everything looked good.

do you know this for sure?

Receipts for the transmission seals. Whether or not the clutch was looked at or not I couldn't say fr sure. Can only go off what he said and take his word for it. He said they told him there was only about 25% wear

What part of the clutch would make this rattle? And why only at those rpm? Shifting and clutch feel seems good for a car this age. Feels crisper than my E46 ever did with much less kms

is this happening while the engine is under load?

if so, could be valvelash?

if not under load,
throwout bearing?

could maybe be the cat? They get rattley when the insides break up. A loose heatshield will also make some rattley noises, which will not be constant.

The rattle sound is consistant at those rpm. But only while driving/ under load. It will not happen if the clutch is pressed or the tranny is in neutral. But you can hear it slightly when letting off the gas and decelerating. Not as loud tho. I should also mention is much quieter in 1st gear, all other gears are louder and much more noticeable.

I don't believe it's that type of rattle. It's too precise and mechanical sounding I think. I wish it was the cat!

What is valve lash?

Am I the only asshole who saw "M20 rattle issue" and thought, "No, no, that's normal operation...."?

check the transmission undertray/heatshield, they are often pushed up toward the trans with just enough room left to rattle. also check CAB heat shield clearance to the exhaust, firewall heat shield, and the cat heat shield.

This wouldn't be normal operation cause it didn't happen before. I know what you mean though, it is a noisy engine but this isn't normal valve ticking or injector noise. its louder and only happens at those stated RPM's


I will check those out, but i still believe it isn't a rattle due to a heat shield etc. wouldn't the car make those vibration rattles if the car was in neutral and while driving? this noise only comes from driving. if you put the clutch in and rev it up it will not make the rattle.


Ill post up a video in a bit here I made.

the heat shields will rattle as the driveline is loaded and twists. Its a common problem in GC subarus, Pull the offending heatshield out, secure it, or push it up/down, and the noise disappears. If it's not a heatshield, you might get an idea of what it is while you;re down there, but don't get too excited until you know.

I assume there's no noticeable vibration except when the rattle is on?

Ya i guess that makes sense. Just seems so precise like a bearing. I was thinking CSB but the sound is allocated more to front of the car as far as i can tell.

No noticable vibration, until i hit about 110kms. I'm not sure these wheels i have on are balanced properly though. but rattle itself is not felt, only heard.