Not a line leak, solenoid to one of your front bags is probably leaking internally, replace both solenoids and it should be good. Cheap and easy fix. Your bags do not sound as if they are leaking as it would do it all the time not just randomly, but the solenoids would, and would be internal so they cannot be leak checked. This happened to mine after putting in new front air struts. One of the new solenoids was leaking internally and came out in 2 pieces when checked. Replaced and all is good now.
