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  #1  
Old 02-25-2017, 02:38 PM
Downerdowns Downerdowns is offline
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Location: Tennessee USA
 
Join Date: Feb 2017
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Mein Auto: 1998 Z3 1.9
Constant rear end hum

Hello everyone, I'm new to this forum and I'd like to thank everyone in advance for their advice. That being said, when I'm driving there is this hum that I can almost positively pinpoint as coming from the rear end. I can hear it as soon as I start moving and goes up in intensity slightly as I increase speed. Engine RPM and whether or not I'm accelerating or downshifting seem to have no influence on the sound.
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  #2  
Old 02-25-2017, 02:56 PM
Blacklane Blacklane is offline
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Location: Springfield, Ohio, USA
 
Join Date: Jun 2011
Posts: 2,290
Mein Auto: 1998 Z3 Roadster
The first thing to try is new differential fluid. Maybe go a step thicker. I'm in Ohio and am using 75w110 synthetic (AMSOil Severe Gear to be exact).
Obviousness, you could have a bad bearing, but new oil often clears-up the issue.
There is also a driveshaft center support bearing that is far more failure-prone than the differential. It's not far from the differential. It's pretty easy to replace (with a rebuilt driveshaft).
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Old 02-25-2017, 04:32 PM
ZEEBOY ZEEBOY is offline
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Location: SW Ohio
 
Join Date: Nov 2006
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Mein Auto: 1997 Z3 Roadster 2.8
Time for my annual negative answer on Z3 rear axel noise. I have owned four Z3's, two roadsters, and two coupes..they all had rear axel noise to one degree or another. As blacklane says, there are things you can do to mask it but I have never completely made it disappear...including replacing one on my first coupe.
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Old 02-25-2017, 07:07 PM
Downerdowns Downerdowns is offline
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Location: Tennessee USA
 
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Mein Auto: 1998 Z3 1.9
See I figured it was just a bimmer thing I was going to have to deal with but it feels like there's an accompanying slight vibration (really more like an odd roughness in the rear that wasn't there before and it isn't a consistent "shake")
What leads me away from a diff issue is the fact that it doesn't really vary with throttle position...it's just there when I'm driving.
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Old 02-26-2017, 06:22 PM
ZEEBOY ZEEBOY is offline
The Arkleyologist
Location: SW Ohio
 
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Mein Auto: 1997 Z3 Roadster 2.8
Good point on the relationship between throtle position and noise Downerdowns....typically the really offensive noise occurs between 50-60 mph in fifth gear.
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  #6  
Old 02-26-2017, 09:02 PM
Downerdowns Downerdowns is offline
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Location: Tennessee USA
 
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Mein Auto: 1998 Z3 1.9
There really isn't a difference between any of the sounds at higher speeds. I did pay better attention to the sound on my drive to work today and it sounds more like when you hold a screwdriver on an accessory drive bearing.
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  #7  
Old 03-11-2017, 09:46 AM
JAY11 JAY11 is offline
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Location: Dallas, tx, USA
 
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Posts: 36
Mein Auto: 2000 BMW z3
Have the same whistling mine is, noticeable at 60. I think I know the source is from the diff. (ever took a ride in those Leyland, Bedford buses, not as loud but similar?) From what I have read it's a known to occur in some Z3s. I don't know what the car has but I am planning on 75W110 shortly. I have read of some who swapped in a diff but the noise never went away-maybe the diffs were were similarly afflicted, IDKFS. Please update if you solve this issue or any helpful info.
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  #8  
Old 03-11-2017, 03:44 PM
nfunk nfunk is offline
1998 BMW Z3 2.8L
Location: New Orleans
 
Join Date: Oct 2011
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Mein Auto: 1998 BMW Z3 2.8L
FWIW,

My '98 Z3 2.8L has a rear in hum at highway speeds cruising, but disappears when I either give it more throttle or let up off the throttle. I got the Z3 around 4 years ago at 18,000 miles and now I have 24,000. I have heard several other people mention this hum over the years.
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  #9  
Old 03-12-2017, 10:22 AM
ZEEBOY ZEEBOY is offline
The Arkleyologist
Location: SW Ohio
 
Join Date: Nov 2006
Posts: 545
Mein Auto: 1997 Z3 Roadster 2.8
Call me paranoid but I have many times thought there is a reason for Z3 axle hum....I retired from the automoblie industry and know for a fact that when certain interchangable components were deemed "boarderline" on performance or noise issues, they were sent to "service" or a vehicle product line that was known to have more inherent ambient noise. I have never seen stats on this, but I doubt E36 sedans had nearly the rear axle noise complaints that Z3 roadster are known for...
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  #10  
Old 03-12-2017, 10:37 AM
nfunk nfunk is offline
1998 BMW Z3 2.8L
Location: New Orleans
 
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Mein Auto: 1998 BMW Z3 2.8L
I wonder if E36 sedans had better acoustical insulation or better isolation of the rear end from the frame to minimize the rear end hum?
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