Intermittent road noise at 50-70mph

[slicksps]

Hi all,

Back to probe your knowledge...

About 6 months ago, while on the motorway at 70, the whole car started to hum unignorably loud. After inspection I found a small bulge in the back tyre. I had this replaced with a good/used tyre and it went away for a short time.

A few weeks later, it came back but at 60... then went away... then back at 70... then moved up to 90 and just kept changing to a different speed (+/- 2mph). The tyres were near their limit so I replaced all 4 which didn't have any effect.

On first replacement, I also visually checked the rear bearings which seemed fine.

I don't think it's coming from the front as the steering isn't affected. It's also only replaced to speed, not revs.

Any ideas? I have a mk3 cl auto and can't wait to get rid of this dammed irritation!

[Mikester]

Crap make of tyres can cause road noises. As can the rubbish roads in the this country.

Suspension top mounts? bushes? bearings? etc?

[slicksps]

I would have thought if any of those it would be constant and at a set speed... and changing tyres would have made a difference.

I'll look into top mounts and bushes, I have no idea what they are yet but will find out shortly.

If all else fails I'll change the rear bearings, they're not expensive and will sort out one suspicion I had about grit in the axle grease... I don't know if that would do it but it would explain why it kicks in at different speeds and sometimes goes away. I need to replace the drums (a few too many grooves) anyway so could do it all at once.

[Len]

Were the replacement tyres brand new? have you experimented with tyre pressures?

[slicksps]

Yup brand new and pre-balanced,

My jack broke while fitting one (luckily fell an inch onto fitted tyres) so I did have to release some of the air and re-inflate to fit with the emergency scissor so indirectly, yes tried that too...

Again though between near bald old tyres and brand new lots of tread (and nearly 1k miles bedding in) the problem hasn't changed let alone gone.

[Len]

You sure its road noise?

have you checked the exhaust mountings? Or heatshields?

Just find it weird that it comes and goes at different revs!

[slicksps]

I may have used the wrong word when I said 'road noise' < still not 100% with terminology

It's so loud and deep that I can't tell where it's coming from.

The revs/speed thing got me too, I assumed because it was speed related, the only parts I know of that move relative to speed are the wheels; everything else goes by revs.

[Mikester]

Not true, wind noise also goes by speed not revs.

[slicksps]

Smart *rse 

To be honest I didn't consider wind noise. Nothing has strictly changed however I have removed and reattached both front wheel arch liners, one to fix the aerial and the other for the timing belt... a slight misalignment would be enough to make a loud noise. It could explain the speed variations however wouldn't show why 5mph speed increase makes it disappear entirely.

I'm still fixed on the wheels, specifically bearings... suspension makes an interesting argument. Different road surfaces equal different vibrations and again different speeds...

I hope it's not the suspension though... I've not covered that in my DIY self-made mechanics course 'aka Mr Haynes and and a ratchet set'

[slicksps]

Just thought I would add here there were two problems which sounded identical.

I laughed at the above idea about wind noise, but then after thinking about it, went over the car and realised my boot spoiler had a slight split in the seam. Cleaned it off and re-stuck it so the flute effect is gone.

Second problem turned out to be a wheel bearing. I had not other symptoms and a visual inspection seemed ok, last weekend it started grinding on left turns, making louder noises at low speeds and squealing the brakes so textbook case. Visual inspection is obviously not good enough, it was obviously a warning. Replaced both bearings and all is wonderful.

While on the subject, just need to slot in my new air filter and I will have officially completed my first major service... on my own and very proud. Just sort out tracking and headlight alignment during my MOT and I'm laughing. (or crying when I find out everything I did was wrong...)