Hi Dave,

If at anytime during the flight, your main tanks pickup(s) is being exposed to air, then that air is going into the UAT. This can be particularly troublesome in a twin main tank install on a Y connector going to the header or the UAT.

If the main tank clunk is not being exposed, then there is a leak under suction somewhere. Sometimes this only leaking only occurs at high power. You can usually see the leaks occuring at some kind of junction (timy bubbles or foam going upstream, either at the tank fitting or at a T fitting or something.

Good luck

Matt