Feedback and bad tone at lound volumes on MK IV

I just had a few quick questions. I am just getting a band together and I am now playing at higher volumes with my MK IV to get over the drums. I'm running my MK IV through a AMPEG 4X12 cabinet and for some reason when my channel volume is at 2 and my output level is at 5 I get a horrible feedback squeely noise when the guitar is muted. No matter how far I stand from the amp. It is a combo and when I run it through the black shadow it does the same thing and did the same thing on one of my friends cabs. So it cant be the speakers it has to be the boogie. So if anyone could help me out of what problem it might be that would be great. I also am kindof dissapointed with the performance of the MK IV at loud volumes. I dial in a great tone at low volumes and when I turn it up it sounds like **** and I cant seem to find a good tone at when its loud. So is this normal for a MK IV or is it just mine
thanks
Caleb

It's a microphonic tube. Get new ones!

It depends also on your drive/gain settings...post?

Mine hates the pull bright on the lead channel at higher volumes.

my settings are

http://www.grailtone.com/tone-settings/mesa-boogie/mark4-amp.php?setting=244

And I don't know if it is tubes I just put all new preamp tubes in a few weeks ago and I had new tubes put in 6 months ago could it really be the tubes already?

Caveat: Just because the preamp tube are new does not mean they are good. Try to isolate by swapping out each one by one until the problem
goes away. Power tubes can make a tinging noise, like someone playing a triangle. It never seems to get to screaming feedback IME.

That's pretty high gain. I bet if you run 7 / 7 or 8 / 6 on gain/drive respectively on the lead channel you'll lose the problem.

zebpedersen thanks a lot you were right it was to much gain. I ran 7 and 7 both pulled and the feedback is gone.