Buzz when using Blackstar Fly 3


I’ve just received my BeatBuddy and I’m connecting it to a Blackstar Fly 3 for practice but I’m getting a buzz only when I connect the BeatBuddy to the AUX input. I’ve tried both the BeatBuddy line out and headphone out. Fly 3 is on batteries.

Guitar alone to guitar input on amp, both clean and overdrive, perfect
BeatBuddy alone to aux input on amp, perfect
Guitar as above and BeatBuddy as above then I get a buzz, slight on clean but unusable on overdrive

BeatBuddy is on included UK adapter. Fly 3 is on battery power. If I touch the BeatBuddy casing the buzz reduces but doesn’t go away.