They normally lower in the back once you turn it off and close the doors. How much the compressor runs on startup can vary but the general concensus seems to be that it shouldn't run much more than 45 seconds. My wife's 08 sport seems to always run less than my 08 LR3 for some reason but both are still certified and have been inspected by the dealer and are running fine. A competent Rover tech should be able to diagnose failed suspension components if you pay them to look over the vehicle. Something like a compressor that "might" be on it's way out get's harder to tell.