I have a new (to me) 620Ti that on exhalation when above water "farts". The exhaust diaphragm vibrates. At any depth underwater it stops. My 600 doesn`t do this and they are of similar designs. I even swapped out the diaphragms but it didn`t make any difference. If I put my finger in the exhaust T and touch the edge of the diaphragm it`ll stop. It doesn`t affect the exhaust effort it just sounds...………….well, like a fart. Anybody have this happen to them and if so is there a fix?