If? I had a small air leak, on the rear suspension, how would I know?

What I mean is?

Would I expect to find the car sat low on one side, if left over night?
Would there be a warning somewhere?
Would I hear the compressor running?

I ask, as when I am driving and come to a stop at lights, sometimes I think I can hear the compressor humming? This maybe normal. but I would rather know before I burn something expensive.

I have had air leaks on RR's before that burn out the compressor if not fixed quickly. This is because the compressor is not designed to run all the time. Some RR owners fit a light to the dash to show that the compressor is running. You can jack the car to it's highest and leave overnight. If one corner drops? You have a leak on that corner