i know nothing about cylinder compression, so i don't know if this is a problem or not. when i turn off my car the engine stops and i hear air leaking out of something from somewhere under the hood. i'm assuming it's coming from the cylinders or the intake, somewhere where air would be pressurised in the engine. is this normal? the air only takes about 3-4 seconds to discharge, then it's silent. i've noticed this since the day i bought my car, but never really thought anything of it. is this something to worry about?