Possible air leak, where do I start?

[Darius]

So, Ive noticed that the rear drivers side corner drops a little overnight. After leaving the car for more than 48 hours, I think passengers side drops a bit too. Where do I start looking for this air leak? I have read about using soapy water, but will this help me find what seems to be a very small leak?
Also, few weeks ago I tried to calibrate suspension with no luck, after car is restarted it goes back to normal. Wonder if this has anything to do with this leak? Any help would be appreciated.