let's rewind a bit and revisit what causes feedback. when the source "hears" itself, feedback is produced. that means the guitar pickups are "hearing" the sound from the speaker and feedback is happening.
i can only assume we're talking about the same type of feedback though. sometimes people describe plain "noise" as feedback only because it pops up when the gate is open. can you describe the feedback a bit? is it a squeal? is it musical at all or just noise? high or low pitch?
i'm concerned that you're at "low gain" settings and it's still feeding back, but i can make a pure clean tone feedback with the right amount of volume and guitar positioning. "loud" is a relative term and it might just be loud enough for your guitar to start a feedback loop.
any way you can record what it sounds like, even with a cell phone or something? are you only using the Input gate (found in the Layout menu) or have you placed gate blocks in the preset?
try this: in a preset that has the feedback, turn your guitar volume all the way down, then turn the gate all the way off (turn the threshold setting fully counter clockwise, i think it goes to -80dB). stand where you perform, then slowly turn up your guitar volume knob. remember, there's no gate so it should start to feed back pretty early. does the non-gated feedback sound the same as before? anything different? how much did you have to turn up the guitar to get it to feedback?
generally speaking, unwanted feedback with distortion just means there is too much gain and/or volume and the guitar is too close to the speakers for those settings. it's physics, there's really not much more to do than to turn down the gain or volume. the technique of muting the guitar can always get better, but volume is volume.
unless that amp is actually amplifying certain frequency notches or adding more gain/power amp distortion to the signal, i doubt it's the amp causing the feedback.
lemme know.
