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      01-10-2013, 07:28 AM   #1
elwesso
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Z4M rattle at hot idle

This issue has happened to me once or twice so far, and I haven't driven the car since then. Car has 49k miles, and both serpentine belts were replaced under BMW warranty. No record of the tensioner, water pump, or other items on the accessory drive being replaced...

The car makes the noise in this video when it's idling after being driven for a while (say over 10 miles), fully warmed up. If you give the engine any bit of gas, the noise goes away. I couldn't demonstrate that too well in this video, but if you hold it steady at say 1000 RPM it sounds smooth and quiet as can be.



The fact that the noise goes away once you give it any gas makes me think it was something in the accessory drive. The car runs smooth and strong. I let the car sit overnight, and I took it out again and it didn't make the noise this time. Here's a video of it quiet.



It seemed like I could re-create the rattle whenever I turned the steering wheel to full-lock..

I did my "civic duty" and performed a search, and I ran across this thread:

http://www.bimmerfest.com/forums/sho...ht=vanos+bolts

I listened to the video in post #7 of the water pump impeller noise, and it sounds pretty similar to the nosie I'm experiencing. The problem with it being intermittent is it's tough to diagnose, so I know I need to try and get it to make the noise again, and get out my stethescope to isolate it.

Does anyone have any thoughts on this? I tried to get my stethascope out and pinpoint where it was coming from but before I got a chance to pinpoint it the noise went away... I'm glad I got the engine to make the noise while I was able to take a video.
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      01-13-2013, 04:27 PM   #2
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Bump...... Any suggestions?
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      01-13-2013, 10:31 PM   #3
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its hard to tell where the noise is coming from by watching the video, i wish i could be of better help.

do your rpm's drop when its making the noise? do you notice any issues while driving?
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      01-14-2013, 06:28 AM   #4
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To me it sounds like the noise is coming from the front near the intake manifold, somewhere on the top. The only thing that's really near that area is the water pump and tensioner pulley?

The engine otherwise idles just like normal, and drives just like normal, which leads me to believe it's not in the engine but rather something external?
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      03-05-2013, 07:33 AM   #5
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I drove the car for the first time yesterday (about 80 miles) and the noise has gotten slightly worse.

I'm starting to think the idler pulley up by the alternator is bad.. While I do not have a stethascope, I do have one of those retractable magnets.. I pressed the magnet against some surfaces, and put the other end up to my ear, and it sounded the loudest when the magnet was near the idler pulley for the alternator. It was definitely quieter when I put it on the hydraulic tensioner, near the water pump, and on the alternator itself.

I'm going to pick myself up an 8mm allen socket, and once I do that I'm gonna take the pulley off and see what the story is.. Since the car isn't my daily driver, I'll take the part off and see how things look..
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      03-05-2013, 08:05 AM   #6
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how many miles on car and have the valves been adjusted?
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      03-05-2013, 08:09 AM   #7
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Car has 49k miles, and I doubt the valves have been adjusted It was dealer serviced up until I bought it. Seeing how the noise goes away once you give it a little gas, it doesn't seem like a valve or internal engine issue, as you would expect anything coming from inside the engine to be a bit more rhythmic.

The car runs strong and smooth anytime above idle, so we'll see what happens.
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      03-20-2013, 05:53 PM   #8
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This issue is continued in this thread:

http://www.zpost.com/forums/showthread.php?p=13674873

Short story: I replaced the idler pulleys on the alternator/PS/water pump belt and it didn't help.
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      03-20-2013, 06:22 PM   #9
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Since you don't know when/if the valves have been adjusted, find a good Indy shop that has done it before and while they have it, ask them to suss out that sound. Sometimes you just gotta pay the piper
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