Pasted clip and got a vid on commercial fleet maintenance.
Check bronze bush on dynamo, when dry or excessively worn they can make an awful noise, it's under the slide over coupon bakelite facing and should have a small felt washer underneath, a good dollop of oil won't go amiss.
I recently had a noise in mine which could be described as a buzzing noise I suppose. It soon disappeared and I noticed the generator wasn't charging. I found the fibre gear had failed and the steel generator gear acting like a grinder until the fibre gear wore out of mesh. Maybe worth pulling back the generator to see if that's the problem.
