My 6 year old daughter's bike has back-pedal brakes, and they make a rubbing noise when the bike is coasting. It sounds exactly like as if the tyre was rubbing against the frame. But it isn't, the noise appears to be coming from the hub.
Is this anything to be concerned about?
How easy would it be to repair? Does it just need some grease?
I've never taken a back-pedal hub apart before so I don't know what's inside.
I buy used bikes for my 2 and 4-year-olds, and I overhaul the rear hubs when I get them. Of four used bikes, two of them made the noise you described, and the overhaul eliminated it.