When do you hear the buzz? Only on shore power? Only on Bluetooth, or also on other sources? Do you have any fluorescent lighting? Dimmers? LED lighting? Try turning everything on and off and see if you can identify the source. Disconnect shore power and run on battery. You get the idea. Anything that uses power could be the interferer. Turn Bluetooth off on everything but one music source.
Interference problems are difficult to diagnose. Good luck!
“You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
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