Howl/whining noise mystery

[1nando]

Hi gents,

so this might be nothing but i'm going to throw it out there for some advice anyway.

I'll start with a run down of my mods which could potentially produce this noise:
Front and rear e'lockers
front ashcroft axles and rear hytuff axles all with HD flanges
ashcroft cvs
ashcroft centre atb
ashcroft mt82 output shaft
my rear diff is also pegged with a GBR utah pegging kit

So i get this very slight howl/whining noise (with no vibration) coming from the centre of the vehicle to the rear (really slight and hardly noticeable unless i brought it to your attention) under very light throttle whilst maintaining speed, soon as i accelerate it goes.
Only seems to happen in lower speeds and not over 70kmph. As soon as i press the clutch in it disappears, soon as i let off the throttle it disappears, in gear going down a steep hill and gaining speed with no throttle it disappears. ONLY HAPPENS under light throttle with clutch engaged! Also we just drove to Melbourne and back over the last week having done over 3000kms with no increase or decrease in noise, its been the same the whole time.

Now i've racked my brain trying to think what it could be. I'm thinking my clutch thrust bearing as it only happens with the clutch engaged during light throttle?? The clutch does have a slight rattle on idle especially when cold but doesn't sound as bad as some others on here have reported. The mechanic (indie) told me last time it isn't to bad for a puma clutch and i do have a second one in there that was done under warranty.

or could it be as simple as the pegged crown touching the brass pad and under light acceleration being noticeable and not under acceleration?

could it be a normal noise from the centre ATB?

ashcroft Mt82 out put shaft normal noise?

also i have no clunking, backlash or movement in the diffs.

Thoughts? Process of elimination i can try?

[Toxic_Avenger]

Not sure if feasible, but have you thought about taking it for a spin with the centre console out? You might get a better understanding of where the noise is that way.

[1nando]

Not sure if feasible, but have you thought about taking it for a spin with the centre console out? You might get a better understanding of where the noise is that way.Ill try that

[Vern]

Wonder if its the centre atb? I noticed my transfercase has a slight whirring noise i have noticed since fitting it. (Full reco box with atb)

[1nando]

I say a howl/whine noise cause we all have different opinions of what a sound actually sounds like.
Does yours happen under the same circumstances as mine?

I know what a howling diff sounds like and it doesnt sound like that to me although i could be wrong...

[1nando]

Wonder if its the centre atb? I noticed my transfercase has a slight whirring noise i have noticed since fitting it. (Full reco box with atb)When you say whirring noise does it do it when your increasing speed or only maintaining your speed?

[Vern]

When you say whirring noise does it do it when your increasing speed or only maintaining your speed?No idea, haven't taken much notice, will have a better listen next time i drive it

[D90 orkney]

I have this whine too. At around 50km and at around 100/110.

I reckon my rear diff is on its way out

mine was doing it before center atb

[Ancient Mariner]

I don't know what your whine is but do know it is not the TBD

AM

[trout1105]

I have had these sort of noises twice on my D2a.
The first time it was the transfer case than needed to be rebuilt the second time it was the rear diff.

[Dorian]

If you've got an ATB centre, check that your tyre pressures are OK.
I've got ATB's all round and my car sounds like it's about to drop a wheel bearing,
- if both fronts are substantially lower than the front (like 20 to 40 PSI - not that i'd ever forget to pump the fronts back up )
- if one side rear to rear or front to front. kicks in at about 10PSI difference side to side.

Only happens when I'm cruising, not under load and the speed depends upon the pressure differences. For me usually happens around 60 to 80 Km/Hr.
Get the pressures right and sound goes away.

Cheers Glen

[Vern]

If you've got an ATB centre, check that your tyre pressures are OK.
I've got ATB's all round and my car sounds like it's about to drop a wheel bearing,
- if both fronts are substantially lower than the front (like 20 to 40 PSI - not that i'd ever forget to pump the fronts back up )
- if one side rear to rear or front to front. kicks in at about 10PSI difference side to side.

Only happens when I'm cruising, not under load and the speed depends upon the pressure differences. For me usually happens around 60 to 80 Km/Hr.
Get the pressures right and sound goes away.

Cheers GlenI have an atb centre, and my front and rear diff ratios are slightly different, would have thought this would affect it then.

[Dorian]

I have an atb centre, and my front and rear diff ratios are slightly different, would have thought this would affect it then.

Fair enough.

I usually run around 38 on the front and 42 on the rear, but once after coming back onto the tar I left the fronts at 18 and put the backs up to 42, got a similar howl as when I get a slow leak on one tyre.
All good after I pumped the fronts back up.

[Dorian]

I have an atb centre, and my front and rear diff ratios are slightly different, would have thought this would affect it then.

Fair enough.

I usually run around 38 on the front and 42 on the rear, but once after coming back onto the tar I left the fronts at 18 and put the backs up to 42, got a similar howl as when I get a slow leak on one tyre.
All good after I pumped the fronts back up.