I use a Korg AX1500G multi-effects pedal, Marshall MG100HDFX head, Carvin V412B head and an Ibanez SZ520QM with Duncan/Ibanez stock pickups. When I use the distortion from the "Metal" setting on the multi-effects pedal, it’ll get pretty loud. How do people like Satriani and Petrucci get a distorted tone where it sounds heavy, but there’s not heaps of feedback and unwanted noise?
Most multi-effects pedals have waaayyy too loud and distorted metal effects. I’ve got a Digitech RP350 and I’ve experienced that too, especially at higher volume levels. You’ve got to play around with the amp and effects a bit to find the right tone that’s heavy, but not temperamental and undesirable. On my multi-effects pedal you can adjust the effect level to make it milder. Also I’ve noticed the treble is really high on some effects, so dialing back the treble on the amp helps too.
Don’t ever add amp distortion to pedal distortion. Use a clean amp setting then add the effect distortion. Also the effects have their own EQ, so probably go with a pretty flat amp EQ and not high gain or bass.
Most hard rock and metal guitarists don’t use as much distortion as people think. This is something I’ve learned over the years, that sometimes less is more.
Hope this helps!