GFCI buzzing on same circuit as dimmer
I have never encountered the situation of a buzzing GFI before. Sounds a bit fishy to me. The trouble shooting procedure would be to turn off the power to the bathroom, unscrew the GFI from the box, pull it out a bit and remove the "load" side wires which should go to the dimmer and check that "line" screws are tight. Turn the power back on, if the dimmer is on the load side then the light with dimmer should be inoperative. Does the sound go away?  If it doesn't and the buzz remains, the GFI is probably defective.  Now turn the power back off, put the load wires back on and test again. If the buzz comes back then replace the dimmer or swap it for a regular switch. If neither of these subtitution tests stop the problem, call a different electrician.  Trust me, a buzz from a GFI or a dimmer is not a normal situation and could be a  potentially dangerous situation. Feel free to ask follow up questions if any of this doesn't make sense to you.  Maybe one of my buddies can do an edit to make this a bit easier to follow.