Loud droning sound from back break

[PsychoPigeon]

My Yamaha YBR has passed it's MOT and had a service recently but something that has come up since then which is a loud droning sound from the back break when slowing down when I'm 30mph and above. I'm not putting my foot down on it but at a certain point it will make the sound so I ease off and apply more front break to make up for it.

It's not a high pitched squeaking sound, it almost sounds like a horn, it's a dull hollow type of sound. I was wondering if I was using the back brake the wrong way. Would this sound familiar to anyone here?

 

[MowyTone]

Going by Google image search your rear brake is a drum brake. All of the workings of this are internal to that drum so there isnt much that can be looked at without taking the drum apart. Has it had new brake pads in the service?

Sounds like something isnt aligned properly. Also look at the position of the rear wheel to make sure it is square on to the bike. Also make sure that the wheel isnt leaning left or right from vertical (could suggest wheel bearings collapsed)

 

[Malt_Vinegar]

I remember reading about YBR drum brakes making noise when they are full of brake dust and contaminated when I was looking at 125s a while ago.
I would strip it down, clean it up with brake cleaner and check it is wearing evenly/as expected

 

[Smok3y]

Was going to post probably brake dust build up.