So u have one submersible pump with 2 tanks running off it? I take it there is a check valve up top somewhere before the tanks and pressure switch? If so, sounds like a hole somewhere down the well in the pump line. so when you build pressure and cut off.. the check valve up top holds pressure and the hole in the pump line leaks out. So when ur pumps cuts back on.. it has to push all the air from the hole to the up top check valve so it blows the air before the water when pump kicks on.