Metallic rattling under very low-rpm load

[alexandre]

Hey guys,

So 3 weeks ago, I replaced the following:

- Water pump, idler, A/C tensioner, belt tensioner pulleys
- 2 belts
- Alternator
- Radiator
- OFHG, VANOS oil line

I also flushed my power steering fluid with Redline D4 ATF, and flushed my coolant completely (block, ET, radiator) and filled/bleeded with BMW Antifreeze 50/50 with distilled water.

Since then, my car has been butter smooth, except for one thing. When under load at very low RPM, there's a metallic rattling that I can't pinpoint.

https://www.dropbox.com/s/44z675ey9f...%2001%20PM.mov

Sorry for the crappy video... but the sound is the most important. I was slowly engaging the clutch in reverse with the handbrake on with no throttle. It essentially happens whenever there is load on the engine and the car is under 1000 rpm. Sometimes happens at idle too (~700 rpm). Besides this noise, the car accelerates and runs perfectly. All fluids are topped off.

I made sure all 4 pulleys were tightened properly and the belts aligned properly as well. I re-tightened everything I could from the top.

Does this sound like something internal to the engine ? It sat with the front jacked for 10 days, and when I started the car for the first time, there was some ticking while the oil re-circulated in the engine. Hopefully I didn't damage anything.

Idea #1: I'm thinking it could be the metal belly pan, as I took it off while I tried to find the coolant drain plug on the block, and I might not have tightened the bolts enough.

Idea #2: It could also be a defective pulley, but stupid me threw the old ones away because I didn't think. There is zero squealing of the kind typically attributed to pulleys. Can I damage anything if I remove both belts and run the engine for 10 seconds to see if it rattles ?

Idea #3: I have the URO aluminum water pump pulley, if it changes anything. Maybe it just vibrates more.

Idea #4: I lost one of the airbox to MAF clips somewhere in the engine bay, and I can't locate it. Maybe it's stuck somewhere and causing this ?



Thoughts ?

[LivesNearCostco]

As long as engine is cold, definitely safe to run engine for 10 or even 30 seconds with no belts on to see if rattling is related to pulleys. But as you noted rattle is not usually from pulleys. Could be loose reinforcement plate on bottom, or the metal MAF clip rattling around. Did you loosen any of the heat shielding or motor mount nuts?

Edit: Just listened to your video, and maybe that could be a pulley noise, so go ahead and try running it without belts for a few seconds. Is it possible you didn't tighten the water pump pulley bolts that hold your old pulley to the new water pump? Or didn't bolt the alternator securely to the OFH? Forgot to tighten one of the OFH bolts? I'd guess there are at least 15 bolts you had to remove and replace, not counting those for the airbox, electric fan, radiator, VANOS line, or PS pump. Maybe left one loose?

[wertyu78]

It sounds to me like a throw out bearing for flywheel chatter. I've had those "noises" for over 20,000 miles and the car still shifts and engages the same. I keep "hoping" it will fail so I can have a reason to install a LWF and m5 clutch. Oh well. No complaints here

[Lespaulman16]

Check the pulleys, check the tightness of the belly pan, but I'll be honest with you, this sounds exactly like TXB/ Flywheel chatter. It resonates like that, too.

Check everything, but you might be okay

[alexandre]

The thing is I've never actually heard that. I thought it could come from the tranny as well, but this clutch has been in there for 40k now... with no such rattling. Could it just happen randomly like that ?

[wertyu78]

Yes. My ZHP didn't have any chatter or throwout bearing noise until 3,000 miles into my ownership. 93,000 miles to be exact. In my case its just a slight annoyance that I've gotten used to. It isn't any issue so therefore I have not addressed it yet. I wouldn't worry unless it's substantially loud.


http://www.youtube.com/watch?v=YyFgTg57j0Y

[wertyu78]

http://www.youtube.com/watch?v=5lgKX4ihtxs

[echo46]

Check the pulley but I'm leaning toward the throw out bearing also.

[Dave_B]

If it's the TO bearing, then you should hear an audible change when the clutch pedal is depressed.

Does that occur?

If it's a pulley, then I would suspect the noise to change with the RPM of the engine.

[alexandre]

No change when clutch pedal is pressed in/depressed in neutral. It gets louder when I depress the clutch in gear, i.e. when the car starts to move.

I'll remove the belts tomorrow morning and start it up to see if it might be a pulley.

Thanks for the responses