Mark IV squealing noise on lead channel

[YtseFrank]

I have this problem while playing at high volume on the lead channel. All my 3 channels are set to have the same output level at around 2 on the master knob except the CH3 which is a little louder to kick in while soloing. This means I have a little more compression on CH3 preamp section (preamp at 5-6 and drive/gain around 7 pulled). Is it possible to keep the same sound/output level without getting this feedback-like squealing noise ?. This channel seems to be very sensitive. It's even worse with EMGs.

Any advice ? modes or settings that could reduce this ?

 

[Rampage]

Are you playing with the Mid-gain or Harmonics voicing? Whenever I start turning the volume up, Mid-gain almost becomes a useless mess of feedback for me. Otherwise, your gain and drive settings don't look too high. Perhaps you have a 12AX7 in the preamp that is becoming noisy?