Alternator Noise

[1Oscar]

My PA28-140 has always had a little bit , but this afternoon it became very pronounced . I use Bose headphones, but carry a cheap non NC ones as a spare. I switched to them, there was still noise but more bearable than with the Bose. I could turn the ALT switch off and 100% of the noise goes away. I cycled the radio switch, the avionics bus, and the main. No luck,

Any ideas? Where do you start??
Thanks

 

[Ray93J]

 

[Tweety]