Humming Noise When Driving Over 100kph

[PAV34]

Basically, when im on the freeway doing 100kph, there is a humming noise when the car is in gear, when i change to neutral and role the humming goes away. I dont know if its coming from the gearbox or the diff, but its a quiet hum every second or so.....hum.....hum......hum......hum.

Any ideas? Im leaning towards it being a diff problem...

I have ruled out the problem being tyres or anything under the bonnet.

[GTR-32U]

Does the humming change at all if you are in a different gear ? Say 4th @ 100 as opposed to 5th @ 100 ?.... If there is no change regardless of gear used my guess would be the diff

[PAV34]

Nahh no change if im in a different gear.

So what does this say about the diff? the car still goes well

[Liquidity]

How long has it been since you got a wheel alignment?

cheap and quick way to rule out wheel balance, hub issues, etc , and most decent aligners will spot any damage suspension issues while they are at it.

Most likely your diff but its somewhat expensive to swap that out.

Edited January 14, 2009 by Liquidity

[PAV34]

I pretty sure its not the wheels. Suspension is only about 18 months old.

Could it be that the drive shaft needs to be re balanced??

[(B1) MR_fanny]

could be the tyres themselves? my old set would hum when it hit 60 all the time every time. try changing to a diff set of wheels if you ahve the luxury to

[GTS4WD]

From what I have been reading and heard from people drive shaft re-balancing is rarely the cause.

I too have a driveline noice over 100k but I was told from another GTS4 owner who had the same problem it was the transfer box.

Does anyone know how to how to assess whether the transfer box can be making this noise?

[Excess]

i always thinks it might be the diff. only happens over 80kms

[blind_elk]

A couple of things happen when you toss it into neutral @ 100kph:

Revs drop to idle (assuming your foot comes off the pedal at the same time!)

Load is removed from gearbox

Load is removed from diff

and in a GT-R / GTS4, load is removed from the transfer case and front diff.

So, it's possible it could be in the exhaust, but that is usually a "drone" (low pitch). If it were in the gearbox, the frequency would vary depending on engine revs (which gear) @ 100kph (hum....hum....hum.... vs hum..hum..hum..). If it were tyres, then the noise wouldn't go away in neutral.

Check fluid levels in the front diff, rear diff and gearbox. Maybe even change them. See what happens.

[PAV34]

I changed all diff and gearbox oils about 15000kms ago.

I notice between 90 - 110kmph is when you can hear the hum.

Not sure where to go from here

[PAV34]

Problem solved!

I shouldnt have spoke to soon, i went to get a wheel alignment and rotate the tyres and what do you know, problem solved.

Which wasnt a problem to begin with.