Harmonic Drivetrain Noise At Constant Road Speed 260rs

[flavzz]

The car has developed a long flowing constant harmonic drivetrain noise. It is road speed dependant and independent of throttle input (clutch in still makes the noise).

The period of the noise is about 1-2 seconds at 60kph cruise.

I have an idea of what I think it is but wanted to get peoples unbiased opinions before I put ideas in your head and cloud judgement.

Car has done 180,000kms. The noise was intermittent but is now constant.

Edited April 23, 2015 by flavzz

[jiffo]

Check tyre circumferences.

Some tread patterns are very noisy and with different tyre wear you'll experience "beats" as the harmonics come/go.

Upset me in the GTR when on very smooth bitumen, and I'm deaf as a post.

New tyres on rear at 1990 circum, good tyres on front at 1985 circum, within 5mm circumferences and noises gone.

[flavzz]

Running federal 595 ss allround with decent tread and no noticeable wear. I will check tho. Any other thoughts?

[niZmO_Man]

They're noisy.

[GTSBoy]

Yuh. Tyre noise. It changes as they bed in and wear down. KU36 in particular are famous for it. I imagine 595s have similar behaviour.

[flavzz]

Interesting. If so the only solution is to change tyres? One thought id had was centre driveshaft bearing which I'd heard can cause noise especially given the kms on the car..

[jiffo]

Certainly centre bearing and worn universals can give high speed vibrations, not usually harmonic though.

I'd check tyre circumferences before anything else.

Note them all for future reference.

Big ones (equal left and right) on the rear, smallest on the front.

If you get more than 10mm difference front to rears you'll hear it.

We deaf old farts feel it.