I have a battery-powered portable speaker that has a USB power tap for a connected player. For the longest time I've battled to rid this power tap of noise. Whatever player I used -- Sony DAP or RPi/Squeezelite -- and however I connected it -- analog wired or Bluetooth -- so long as it was taking power from the USB tap it was ruined by noise. I just got this little device for very small change and it solved the problem:

Mpow Ground Loop Noise Isolator Car Audio System/Home Stereo With 3.5mm Cable