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Discussion Starter · #1 · (Edited)
Few weeks ago I noticed a slight metal rattle noise coming from under the hood and tracking it down seems to be a huge mystery.

My observations:
- It sometimes makes the rattle when the car is started on a cold morning, other mornings it'll start without making the rattle.
- It sometimes makes the rattle when the car is turned off, other times it'll not make the rattle at all when the car is turned off.
- Only happens from ~1krpm to ~1.6krpm and very random in between those rpms.
- The rattle seems to be coming from the timing belt side of the car.
- Seems to only happen when I press in the clutch pedal and rev the engine, if all I'm doing is revving the engine without touching anything else it doesn't happen.

Recent fixes/stuff already checked:
- New Clutch and Flywheel were just installed this week, I thought that was going to fix it but it didn't. At least it has that going for it which is nice. :D
- Timing belt dampener seems to be okay, it was replaced a year ago when I put on a full timing belt kit.
- Pulled the valve cover and everything in there was b-e-a-utiful.
- All of the motor mounts are going to be replaced shortly since the old ones are pretty bad and cause too much vibration.

Some questions:
- My A/C compressor has been dead for a while, but I don't see why it would make noise all of a sudden - especially in a specific rpm range and with the clutch pressed in?
- I have yet to replace the gear oil in the transmission, possible it's something in there that's causing the rattle?

I guess the biggest question I have is why would a rattle occur when I give it some gas with my foot pressing the clutch but no rattle when my foot is off the clutch? (I had the car in neutral when I tested this.)

Other than that, the car drives pretty well.

Perhaps I'll try taking a video/audio in-case that'll help.

Thank you!
 

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Using a mechanics stethoscope; can help isolate noise many times.

https://www.google.com/search?q=ste...119&ie=UTF-8#q=mechanics+stethoscope&tbm=shop

So, did you replace the clutch/dual mass flywheel with stock parts or aftermarket single mass flywheel conversion?

Have you checked the alternators clutch/oap pulley and see if it is damaged or seized? You can learn more by checking out this thread:

http://newbeetle.org/forums/1-8-lit...-failure-what-best-brand-replacement-buy.html

A really basic way to isolate things; is to remove the serpentine belt and see if the sound is still there, if it goes away... check each component on the belt path to find the offending part. If it is still there; then you have eliminated the whole belt path and related components.

Sometimes; it helps to put the car on a lift; while running and then, be able to try to isolate the sound from that vantage point, a mechanics stethoscope is handy as well. Having someone else; by your side or checking it out.... is always a good idea! A fresh "pair of eyes"; can be helpful, since you can have "troubleshooting fatigue" when trying to find a problem for a long time (you can lose your objectivity). Hope this helps!
 

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Discussion Starter · #3 ·
My friend does have a mechanics stethoscope in his tool collection - not sure why I didn't use it when we last took a listen.. oh momentary lapses of reason.

I'll definitely have to try it out soon to try to get to the source of the noise.

Belts rotated fine and tension seemed fine on both so that's why we dove into replacing the clutch/flywheel since it was way overdue anyhow.

I was hoping it was the old flywheel that was making the noise but when we pulled the transmission off, we were surprised to see that the previous owner put a single mass flywheel. I knew right there that the noise was definitely not from the flywheel anymore. We installed a Dual Mass LuK brannd flywheel and clutch and there is pretty much no more chatter coming from that area which is super nice - shifts like butter too. xD

Removing the serpentine belt sounds like a good idea too, that way it'll be obvious if anything belt driven there is causing it. I plan on installing a working AC Compressor for the summer so that whole area will be thoroughly inspected soon.

Thanks for the tips! I will update this thread with my findings/fix once I figure it out. :)
 

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sai pump

I had something similar a year ago it was the Secondary air injection pump rubber bumpers they rut out and the pump rubs against the metal support and makes a rattle noise, especially on cold mornings when you start the car like you specify. It has three of those supports and you can buy those on ebay for a decent price.$7-8 bucks.
 

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Discussion Starter · #5 ·
It'll actually make the rattle on warmer days even after the car was driven for a good while. Usually it'll only do it after the car was off a bit, say I go into a store, then fire it up and put it into first it'll make the rattle then disappear.

Reproducing it lately has been ridiculously tough. I got one of those stethoscopes but we've had no luck figuring out what it is.

My secondary air pump has been finicky for a while but I'll double check the supports just in-case!
 

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Discussion Starter · #6 ·
Update on random rattle issues; this is not 100% but the noise went away for the most part shortly after my last post.

Installed new motor mount, transmission mount, and put new bushings into the dog bone mount and the car handles like a dream. The old motor mount could be separated in two whereas the new one is firmly held together.

I believe this should take care of the rattle issue - 145k on original motor mounts - definitely needed replacement. Was kid of scary seeing how the old mounts were like compared to the new!
 
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