Hey there - I'm noticing a very considerable difference in level when connecting via the g90 vs. connecting straight to the amp. This is detrimentally increasing the noise floor and causing a great deal of squealing and feedback through the amp.
I've moved things around the signal chain and tried alternatives with gain structure and am confident this is not the issue - the only variable that seems to change output level is the line 6 g90...
I'm not currently utilising the 'cable tone' setting on the g90.
Signal flow is - Guitar>
Line 6 G90>
Line 6 Pod HD500x>