The Noise has returned, could do with some thoughts please.

[911hillclimber]

I have been through this once before in some detail, but would like to discuss the events of yesterday and today in my 987.2 2.9 Boxster.
Let's hear what you think as I'm at a loss.
A few salient details first:
987.2 Boxster, 91K miles, mine for the last 10 years.
2009 (March) full service history, does around 5K miles/year. Had the transmission oil changed about 6 years ago as part of a major service at Zuffenhaus. (who service the car now for 6 years, maybe 7).
Used for touring, rarely red-lined, no track drives etc.
19" rims Bridgestone tyres, same grade on all corners and N rated. 32 psi Fr and 34 psi Rr. Fr tyres are 6 years old and lots of tread, rears are 2 years old, and lots of tread.
Exhaust is the original unit from new and is fine.

We have just been into deep Wales, 280 miles round trip, overnight stay. Up until this pre trip point the transmission/car were normal, lots of road noise and shift action a bit heavy but fine.

The Noise:
A hard humming starts at 41 mph (very repeatable) seemingly in the rear and continues to about 60 mph when I think road noise is louder so drowns the humming out.
Did this for the last 2 days.
The humming happens with the engine on load, or off load or just keeping the car moving at the speeds. Gears choice makes no difference. Will do it in 3rd or 6th etc, makes no difference, thus I think the engine/clutch has nothing to do with it. You cannot feel any harshness/vibration in the chassis.
Going round turns gently or hard in the 40/60 mph speed range the noise does not change, so feel wheel bearings are ok.
Apply the brakes at 60 (say and gently) and the noise just runs down until 40 mph and it disappears.
Slow turns in reverse and forward, no CV clicking, all silent and smooth as it has always been.

Last time I had this same thing was before the rear tyres were changed when I had the wheels refurbished, so 2 years ago. It came on suddenly then, just as yesterday.

The tyres then were quite worn, far more worn than the current tyres. (they were Bridgestones, same spec as now)

This all points to the rear tyres, but any other thoughts please?
Thank you.

It is VERY IRRITATING.

The fresh tyres seemed to silence the issue, but now, 2 years on it is back.

 

[stephentodd]

Hi there, are the tyres worn evenly across the rear tread? Is the alignment spot on? if you rub your hand across the tread does it feeel okay? Not feathered or uneven?
I had a similar situation on my Boxster & the tyres weren’t smooth, they were uneven, you could feel that they weren’t right.
Full alignment & 2 new tyres the noise disappeared. The previous alignment was only a couple of years old, so something had shifted been pot holed out of true.
Hope this helps.

 

[911hillclimber]

Than you for your reply Stephen.
The car's tyres are perfect, even no feathering Fr or Rr and chassis re aligned last year after the front coolent pipes were changed for new.
Car runs hands-off.
Common factor is the rear tyre new v used.

On ebay i can get 2 new tyres for £130 which would be a cheapish experiment to change the Bridgestones over to the ebay tyres and drive it.
If the noise goes then it is the Bridgestones...

 

[Scrounger]

I’d have said wheel bearing but if you say the noise doesn’t change when turning then I’m a bit stumped. It would be worth getting the bearings checked or you can check them yourself by jacking the car up and wobbling the wheels.

Dan.

 

[911hillclimber]

Thank you. Did all those checks last time (about 4 years ago) and they are super tight, smooth and noise free.
Wheels coming off soon for pre-MoT jet wash so can check again.
Someone else has suggested wheel balance.

 

[CLIFFWILKINS]

Sounds like tyres again very weird I know .
Try to swap the wheels with a good samartan just to test.
All the best hope you get to the bottom of it.
Regards Cliff

 

[Timrice]

The symptoms sound similar to a problem that I had with a Golf a few years ago. It was identified as Sawtooth Tyre Wear, which seemed to be caused by the combination of tyre type, tyre wear and suspension geometry. I am not sure whether this matches your circumstances, but it might be worth researching it.

Good luck.

 

[911hillclimber]

Over on DDK forum, someone has had the same issue albeit on a Subaru Impreza. Bridgestone tyres at fault.
Seems the tyre has two compounds and when the tyres get to the transition of outer compound to underside compound the noises appear.

This could answer when new all is good (as it was in my case) then they deteriorate.

The car drives perfectly, corners, brakes etc well will has this noise..

After all the pot holes over the last 2 days in Wales I really wonder if a good sports car has any appeal. My wife's Skoda Citigo would ride them better.

I am facing i think at least changing the rear tyres to another manufacturer and then the fronts later if the noise disappears.

I don't like mixed tyres on a car, but at least the tyres across the axles will be the same.