My rear tires are almost gone but they have been pretty decent in terms of noise(Michelin Diamaris )
Well lately, I've been noticing some kind of tire noise that increased with speed...don't know exactly how to describe it but sounded like a really worn tire that has a huge metal screw in it...at speed, you can get an idea of what it sounded like...
I narrowed it down to the left rear tire, went and checked it and sure thing it cupped in the middle...put a level on the tire and I noticed a gap of about 1/4" ...checked the right rear one and it was perfect...
I guess my question is : what causes this?
Worn suspension components?
Too low/too much air in the tire?
The noise bugs me to no end so any opinions are welcome.

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2006 X5 4.8is LeMans Blue / creambeige interior
Prod.date: 2006-06-21