I like to update/conclude a thread I started in hopes of helping someone else one day.
Did a few things today at the hanger and it turns out that my brand spanking new Zulu 2 is the problem. No radio interference or squealing in the other headsets I tried. The power cord, XM antennae all produced no problem despite their placement.
Go figure !!
It's like a post I just finished reading on a rough running engine. The fella rebuilt his mags, changed the plugs and dang near rebuilt the engine trying to solve the roughness. Turned out that 2 of the brand new fine wire plugs he bought were faulty

Harder one to solve.
Darren