I have a feeling this has been discussed here but I cant seem to find the thread. I have a 2006 2.5T which we got with around 165k on the clock. Apart from the normal servicing every 9-10k, the only drama I have had with it was the prop shaft universal joint grease drying up and making loud noises (too close to exhaust). Then there was the occasional harsh gear downshift. I fixed this with a few transmission fluid drain and fill as discussed in a previous thread - gearbox works very well now :)
When I got it, there was a slight whine/hum that was evident between 60-80kph then disappear. You had to really listen for it...but it was there and definitely only under load. It never bothered me as it never got any worse. The car has now done 45k - all country highway kms - since we got it, and during its last service, all 5 engine mounts were changed. Also, the rear tyres required replacement so we rotated them and new ones went infront and old ones (70%) went rear. Immediately I picked the car up from tyre guys, I noticed that the whine/hum was definitely louder and now happening from 60kph to around 110kph. Fluid in front Diff (bevel) was changed almost a year ago. I haven't changed the rear diff fluid yet.
I guess my question is how do I tell which diff is making the whine/hum and generally, what are my options? I'm almost certain its a diff because you only hear it under load. Will refreshing the fluid make any change or has the bearing already had it?
Cheers! - Steve