Major or Minor Suspension Problem? - 2006 3 Series Estate

[Lomardy]

I noticed tonight that on the drivers side of my car at the rear the body seems to sit approx 1-2 cm lower than on the passengers side. I had a look behind both wheels and just before the suspension strut goes into the body (and is concelaed) there is some red/brown casing, below this is some black casing. On the lower side there is about 1-2 cm less of the red/brown casing showing. It looks as if the black casing might have slid up over the red/brown casing although I am not convinced this is what has caused the smaller gap between the body and top of the wheel on drivers side. Could a bushel have come out at the top?

Not the best description but does anyone have any idea what the problem might be? Would it be covered under warranty?

Any advice would be appreciated.

Thanks

[HarryW]

Does it have self levelling suspension, if so the 'air springs' could be failing on that side.