dan
2
Hi @Lucy and welcome to the forum!
Take a look at these videos; they are coming from a power station perspective but are still useful. I’d first see if this is a ground loop.
If you unplug everything from the UL so it’s just guitar in and speaker out (no FX, no pedalboard) do you still get the same feedback?
Also how close to your amp are you standing? Could this be feedback caused by your pickups being too close?
Let’s eliminate these possibilities first.