I own the micro station BT as a monitor controller for my ES-9 euro rack modular interface - which lacks a volume controller for the main output) and I use the bluetooth feature extensively. My monitors are presonus eris 6 pro and everything is connected with balanced cables and supports balanced in/out
I have a ground loop noise that is not affected by the Microstation main volume control knob - it becomes evident as soon as the modular system is turned on - even if the microstation volume is muted and knob is at zero.
This makes me think the problem is electrical in nature. It sounds like noise with a high pitched whining component - like USB noise.
I realise this is common and I have tried some simple things with no effect (trying different power sockets etc)
Removing the microstation from the equation definitely improves things. I guess it has an amplifier which is boosting the bluetooth/line in signals and therefore electrical noise?
Is there any USB power cable ground-lifter or similar device that I can try on the USB power cable?