Probably not much, since Bluetooth is radio, and "sizzling" is part of a noisy connection. Try connecting to another device (phone or computer) and see if you still hear the noise at full volume. Connect different headphones to the A7 and see if you still hear the noise at full volume. Then
register an account and come back here and tell us what you found and we can try to help you further.
(Also try making sure that the phone is on the same side as the earphone with the radio - Bluetooth going through a whole human body thickness is close to being out of range.)