The UAT sucking in the sides and the pump voltage concerns me--I know that this larger engine is going to require more fuel that my Mercury HP, however....My pump voltages for a typical flight are around 3.5 to 4 volts MAX!! That pump voltage does seem high. You could connect the pump up to a 4.8 to 6 volt power supply and break in the pump. Of course you will be breaking in the pump using filtered fuel and never allowing the pump to run dry. Are you running a fuel filter between the pump and engine? (You should) If so, what kind??? I use the high volume clear Festo filters. A small fuel filter can cause a restriction.

Does the turbine spool up freely?? I know that there were some bad bearings in the AT-400's. (Rough/bad/defective bearings can cause high pump voltages.)

As Craig suggested, take the engine out to see if the problem is the bypass. (The only negative thing I have ever witnessed concerning a bypass was that the plane was slower in flight than without the bypass.) Those whistles--Could they be mistaken for a harmonic noise??? My Mercury made a high pitched whistle when new and it turned out to be caused by harmonics...Re-balancing took care of the issue.

Kevin