Glad you got it fixed.

I'm confused though... You said you were grounding the flasher? I mentioned the mounting stud might not provide a good enough ground and there was also a ground wire as shown in parts diagram. So I guess you weren't actually grounding the flasher? Oh well, as long as it works now.

Thanks for the 'thanks' 'on previous page' but i'll pass that over to MarkT as im sure he said it earlier that the metal body of those units need earthing.
Yamaha tricks are sent to try us haha.
I think Mark also said something like,--reading how you earthed it doesn't quite add up, but possibly just everything getting 'lost in translation as they say'.
Flasher unit body has a good earth & that's the bottom line.
Funny thing though listening to the video of it buzzing brought back memories of exactly 'that' with those when not earthed. & as i think Mark said--lucky if you don't get a shock off it--if you sent it to earth through you by grabbing the frame to earth it.
Anyway--we'll be coming to you for advice after all this is over--let's hope it's over for you & top marks.

Not sure I understood what earthing really meant before. The metal bracket that holds the flasher was grounded to the battery tray which I made sure had a good ground to the frame. What fixed the buzzing was the earthing wire from the same mounting stud plugged into the wiring harness ground circuit.

Of course thanks to Mark as well he explained some things too that helped me out. I really appreciate the info found on this forum!

Yep i guess it should've worked if the battery tray was earthed & they're normally rubber mounted i think, but separate earth to the frame from battery box should have sorted it as you said. Can only think paint on the b-box & frame were getting in the way of a good earth. Never mind, good its working.