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987.2: Trouble again!
- Thread starter marc_tt
- Start date
AndrewT
Member
I hope you find it whatever it is.
Recent cold start smoke has dissapeared but, another issue has taken its place of course.
At the very end of our Euro tour when the plug tops failed in Austria the car was driving well but a background hummm had started.
I chose to ignore it.
We are now pondering that humm, not louder, and is the subject of this post, may need some help.
All tyres are good, correct pressures and the car straight as can be. Very nearly 80k miles, last 45k with me.
From about 30 mph to aroundd 50 mph there is a drive train humm.
it varies with road speed and is independent of the engine speed or gear.
It is there no matter what the road surface.
There are NO vibrations at all just this hum that is louder than the engine cruising.
Appears to be at the rear.
There are no cv joint tick tick ticking and no play of wheel bearings at all.
There is no noise putting the power on or off, so seems nothing is loose.
Never ever done this before, on my third set of rear Bridgestones and fronts are replaced twice.
All have great tread depth.
So...any ideas or experiences please?
AndrewCS
Active member
There is no noise putting the power on or off, so seems nothing is loose
Not drivetrain if independent of ^ these ?
There are NO vibrations at all just this hum that is louder than the engine cruising
As AndrewT mentioned, something affected by airflow - windspeed ?
Air duct - shroud - trim ... loose - foreign body present ? You may have to remove the engine covers to inspect ...
The 6 plug tops were changed after the Eurotrip by Zuffenhaus during a slightly premature 80 k service. However, would be good to check.
I changed the air filter after the service. However, the start of this hum was in Austria, before any plug tops etc, so suspecting the wheel bearings.
Going to carry on with the car to see if it gets worse which may then give a clearer pointer to the culprit.
Will probably return the car to Zuffenhaus for an inspection of the cvs and bearings and check if anything else is amiss.
Odd that there are no vibrations etc from anywhere, runs a dream above 60 mph, but road noise could deafen the hum.
Another source could be a moaning final drive, although you’d expect to get that on lighter throttle tip-in tip-out.
All very difficult to diagnose without some indication of the frequency of the noise … discrete or broadband?
Jeff
Anyway getting to the point he changed the rear tyres even though looked ok
Whine hum gone.
Try to borrow a set of rear wheels from someone give it a try.
Good luck.
I have a good friend with a 996 C4s so will ask.
Im leaning towards the tyres.
absolutly zero play on the wheel bearing when gripping the rear wheels by hand in the old school way. Handbrake off!
swerving the car leftright at 40 with humm noticeable, smooth road, engine in 5th, sound does not change a single note.
slow tight corners i.e. Car park, and no cv joint ticking, no noises at all.
I had the rear wheels off after the Euro trip but could see nothing on the outside Walls or tread face.
Cold this morning in Scotland, pressures are 32 psi rear, 28 front, but doubt those would cause issues.
Just a thought but if you can get a nitrogen fill that may have a positive effect on your problem as it will have an effect on the tyre cavity mode of vibration. Much cheaper than a new tyre![
Jeff
Tyres are about 1/2 worn, but no older than 2 years.
I had thought of changing them side for side so rotation is reversed.
A/C not on or used but tried it today to test, no difference.
throttle on off, hard or gentle, nothing changes
round bends at 50 or any speed, nothing changes.
no vibrations felt at all, none.
have had this car for just over 6 years, this is new.
will jack the car up this weekend.
hand rotate each rear wheel to check the wheel bearings for play and noise.
check the drive shaft cvs for anything and that the shaft floats axially.
check any covers are not open or loose, but this humm sounds more mechanical that whistle.
change wheels over side for side, road test.
if no change, book the car into Zuffenhaus for check over.
if no change, sell it.
It is hard to justify this car when it keeps giving me grief.
![](https://i.postimg.cc/8C6gpSLb/P1080806.jpg)
Jeff
Good bit is the tough bits are really good, the bearings and the drive shafts.
tyres are a consumable, so I will probably driver the until they are worn, and replace.
Looked at selling the car.
very hard to find an alternative at the same price....
got a small belch of smoke on start up to test drive the car..typical!
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