First of all, I don't want anyone dissing Crate, I love their Flexwave preamp due to it's amazing Metal tones.

Second, I don't need a new amp, I just bought it for 65 bucks with a Fender FM65DSP trade.

Well the issue is that, I had band practice sunday night, and I set the amp up like I had my Crate GLX Stack. I wish I hadn't traded that stack, but that's old news. So I turned the volume up to around 4-5 to be heard over the drummer, and I get this feedback, the kind if you're facing the amp. But it wouldn't go away, and every time I wasn't playing it was there, loud and annoying. I would walk around the room and move my guitar, and could almost get it to stop for a second, but it just changed frequencies and wouldn't stop unless I hit my killswitch. So those nice chugs with breaks for the drums will be impossible unless I'm super fast with my killswitch.

I'm not so sure the Insert still works, I tried a 1/4" to 1/8" insert cable with a 1/8" to 1/4" adapter with my Tube EQ Pedal, and when the pedal was on and off, the only difference was volume.

How can I fix this problem?
I got some good guitars, yo.
Well I turned my volume to like 1.5-2 and it sounds decent with minimal feedback, but I never had this problem with my Crate GLX1200H stack. Is it just due to improvements in how it's made? Because I don't want this to be a permanent solution.
I got some good guitars, yo.