I think the assumptions may be correct - it's likely to be your tyre.
Have you any way of lifting the rear (i.e. do you have a centre stand?) as the most obvious thing to do would be to spin the wheel and listen for any noise - by having the wheel spin EVERYTHING that is normally being moved when the bike is running along will be moving so it could easily be narrowed down.
You say it's not the pads? When you hear the noise try applying the rear brake - if after that the noise stops then IT IS the pads - they could be rubbing when they are in a particular position - did you grease the pins when you replaced the pads so that they can return easilly?
It's simple really to eliminate things - if nothing is rubbing on the wheel / tyre, the brakes / disc isn't rubbing, the wheel bearings aren't grinding, the drive belt is running smooth and the back axle pin is ok then it could only be tyres. If, as you say, the tyre is in need of replacement anyway I would just bite the bullit and get it done.
Would be nice to get your response to what it is when you do find out
Last edited by Botty; 01-09-2020 at 08:18 AM.