Found if you turn up the receiver volume and have the phone volume set low, there is a bit of a "buzz" similar to what you would get from bad shielding on the connecting cable or from a ground loop, even though both the receiver and the adapter were plugged into the same outlet to minimize the chance of a ground loop occurring. Possible the AC adapter may not have enough filtering in it to remove all the AC ripple from the DC out. Did not take time to check that possibility.
As is, it was sort of okay (not totally for serious listening) if you turn the phone volume almost to max and keep the receiver volume low. It is then harder to hear the problem over the music.
If that does not take the problem to an acceptable level, then maybe a different blue tooth adapter would be worth a try?
Good luck.