Rubbing Noise / Low grinding / scraping noise

[celicability]

This noise is only evident after about 30 miles continued driving like motorway but then dont go away till everything cools down again

Sounds like something at rear is scraping / binding / squeaking

Had car on ramp / both rear wheels turn good without any noise or stiffness

Could it be parking brake related / something not releasing etc / handbrake works fine

Around town / low mileage journeys noise never appears

Mot shows advisory rear brake fluctuating but not excessively off side if that helps

Any help appreciated ?

[celicability]

slightly bent out the stone guard behind rear offside brake drum which was rusty hoping it was that scrapping when it got hot / keep you posted either way if it works or not