Possible diff noise ? Solved .

[Greg 01]

Hi guys .
Recently I can detect a noise from the rear end ,carnt quite decide if it's road noise or diff .
You do have to listen for it and seems to get a little louder at 60 mph .
Is there anything I can put in the diff to help the noise ? Was going to do a diff oil change and I read about people using friction modifiers such as red line etc .
Does anyone know if these will help ?
Cheers guys .
Greg

 

[MACK]

Hi guys .
Recently I can detect a noise from the rear end ,carnt quite decide if it's road noise or diff .
You do have to listen for it and seems to get a little louder at 60 mph .
Is there anything I can put in the diff to help the noise ? Was going to do a diff oil change and I read about people using friction modifiers such as red line etc .
Does anyone know if these will help ?
Cheers guys .
Greg

To be honest you may well be jumping the gun a bit here. Although it's fair to say diff noise is more common on n series engined bmws than the earlier m series cars it's still fairly rare and the least common thing this could be.
Have you done all the tests you can on the road. For example driving the car down yge road then dropping in and out of gear, clutch in and out, accelerating, decelerating, trying different gears at the same road speed. I'd do this sort of thing first to try and definitely diagnose it as the diff before spending any money.

 

[Greg 01]

Hi mack.
Thanks for replying .
My car is an auto .
I've done all the slowing ,speeding up . Round corners in and out of neutral etc .
The noise never goes away and gets a little louder at 60 . Drop to 55 and it's almost not there go up to 70 and it's almost not there . I've recently had a geo and put more air in the tyres,then put less air in and no differance then same speed in different gears and no change . Only time it's changes is at 60 mph in any gear .
So I've ordered some sound deadening for the boot and as it's never had a diff oil change I thought I may as well do it that's when I read about friction modifiers ..
Greg .
Forgot to add both rear wheel bearing replaced about 12 months ago .

 

[MACK]

Hi mack.
Thanks for replying .
My car is an auto .
I've done all the slowing ,speeding up . Round corners in and out of neutral etc .
The noise never goes away and gets a little louder at 60 . Drop to 55 and it's almost not there go up to 70 and it's almost not there . I've recently had a geo and put more air in the tyres,then put less air in and no differance then same speed in different gears and no change . Only time it's changes is at 60 mph in any gear .
So I've ordered some sound deadening for the boot and as it's never had a diff oil change I thought I may as well do it that's when I read about friction modifiers ..
Greg .
Forgot to add both rear wheel bearing replaced about 12 months ago .

Is the noise a metallic whine or more a low humming. The humming would point to tyres and wheel bearings where as the higher pitch whine would indicate the diff. Although a diff tends to get louder and louder with more speed not louder at a specific speed and then deminishing . What tyres you running on the rear and how much tread is left?

 

[Greg 01]

Cheers mack .
I'm running rainsport 3 all round the rears are a little low on the inside edge hense the recent geo . That said on my way home today I was messing with different speeds etc try to pin point it etc and I now don't think it's the diff I think it's excessive road noise from the boot area .
I lent down in the car while moving and noticed I couldn't hear it
Very odd so I got it to 60 lent over and bugger me it's gone .
I must have looked very strange as I kept leaning down in the car with my head cocked to one side
So as I've ordered some sound deadening I will do the whole boot and go from there .
Thanks for the help
Greg .

 

[Greg 01]

Hi guys .
Well I stripped out most of the boot and put sound proofing everywhere I could and although it has helped the noise is still there
I will try get it on the ramps and have a look .
Greg .

 

[Greg 01]

Hi guys .
Two new rear tyres and a quick clean and lube of the rear brakes solved this for me .
I would never of guessed it was the tyres making the noise till Mack made the suggestion .

 

[MACK]

Hi guys .
Two new rear tyres and a quick clean and lube of the rear brakes solved this for me .
I would never of guessed it was the tyres making the noise till Mack made the suggestion .

Glad you got it sorted and it was a quick fix at reasonable cost. Tyres can be funny things. It's amazing the difference between a worn and new tyre sometimes, even if they're exactly the same brand and type etc.

 

[Greg 01]

Yes cheers for that Mack .

 

[AlexP]

Hey Greg,

Thanks for posting your solution. I have the same problem currently with my 2008 2.0 m sport.
Its the constant noise and I stuck my head out of the window too haha you aren't the only one.

I was thinking it was either the bearings, differential or the tyres, but since i have old chinese 225/40 R18 rear tyres, im thinking to replace the 2 rears with 255/35 R18 Michelin Pilot Sport 4's. Since for yours it was the tyres, i assume I have the same issue!

Alex

 

[Greg 01]

Hi alex
Sound like the same kind of thing !
I would not have put the noise down to the tyres at all and couldn't pin point it . Drove me nuts for a couple of months
Just got back from a drive out and the car feels great and the noise has completely gone

 

[Z4M-2006]

On cheaper tyres the actual rubber quality changes as the tyre gets lower, tyre techs call it "pudding"...

Expensive tyres will have consistent wear and grip rate until the reach the wear bars, cheaper stuff won't..

The uniroyals we fitted to a fleet of vehicles had the exact characteristics that the OP described.. as well as chamfering off on the inner and bad wear life ...