On my Liverpool clone. I got loads of good advice here, concerning lead dress, pre-amp tubes, etc.
I changed V1 and V2 for some old ones I had, and the high-pitched whine stopped! I wasn't using the same guitar that night, but that wasn't a factor, was it?
Next rehearsal, I'm using the Fly again, and the whine is back...
These amps are very sensitive to things that other amps do not enhance.
My test guitar is an old beater strat and kept hearing that hiss every talks about. Well, tried some humbucker equipped and more shielded strats I own and hiss is tolerable. Go figure. These amps are beasties alright.
captain_rusty wrote: Next rehearsal, I'm using the Fly again, and the whine is back...Solution: CHANGE THE BATTERY.
Does that mean you had a low battery in the Fly causing your whistle I'm interested because I have a Parker Fly as well
Apparently, yes. With my Patrick eggle the whistle was absent, and when I plugged the Fly in, it came back again. 5 minutes later, the tone went all gnarly and then cut out, the standard dead battery symptoms.
I put a new battery in, and the whistle had totally disappeared...
Considering that I just about never use the piezo pickup, I was wondering about rewiring it point to point and eliminating the piezo/battery. I could easily add a coil tap option that way, too...
Don't feel bad Capt. I once spent about an hour looking for an oscillation when I mismarked a cable I'd just made. I labeled it "guitar" when I made up a speaker cable.
I'm interested because I have a Parker Fly as well 
