High Pitch Pulsating Squeel in Stiletto Ace Combo

[Dusty Rhodes]

So I switch on my Stiletto Ace Combo tonight and I hear this pulsating high pitch squeel. The volume as always during start up is at zero. When I started to turn the volume up just a little the squeel dramatically increased. Sounds like an old Sci-Fi movie. This came out of nowhere. After studying all of my connections including my EFX loop I noticed that when I unpluged the Return EFX jack from the amp back the squeel stopped. I'll call Mesa tomorrow but thought I'd run this by the Board first.
Any clue as to what is going on?

 

[Platypus]

Microphonic preamp tube

 

[Dusty Rhodes]

Microphonic preamp tube

I just read the FAQ regarding the microphonics. Would this still be true given that the squeal goes away when the Return jack is disengaged?

Thanks,

 

[buddaman71]

You didn't by any chance have the send and return cables swapped did you?

I have done that on a dark stage.

You could get a feedback loop if your effects I/O to the FX loop is not quite right.

Just a thought.