More questions...
Did you try using another Bluetooth source like a phone?
There are external Bluetooth receivers designed for working with mixing consoles that are nifty and get the receiver away from the mixing board and carry audio via balanced audio back to an equipment rack. But, this... It seems like it may be rack noise causing issues or the laptop itself screwing things up.
Bluetooth is sh1t overall.
It is MUCH better to recommend and use a wired connection if at all possible. You will get cleaner sound and if video is involved, proper lip-sync. Plus, you don't have the limited range of Bluetooth to contend with.
EDIT: I'm also wondering what volume things are set to? Bluetooth volume should be turned up potentially on the computer, or at the mixer... some imbalance may be pushing more noise into the system. So, that's something to play with.
