Metallic scrabbling noise

Hello to everyone

i have this annoying noise is on the front tyre , when am driving the car the noise comes after 15-20 minutes drive not when I just start 

driving like a metallic scrabbling noise is not loud but if you drive for half an hour becomes louder is not the bearing took it to a garage yesterday to put back break pads the front are ok at the moment the mechanic turned the wheel by hand front right and he heard the noise he cleaned the dust that was around ( took the wheel off) then took the break pad off cleaned it and file it a bit he put some Grease he turned the wheel again and all good couldn’t hear anything , when I left the garage after 20 minutes drive I could hear the noise again I think the noise become when all the metals become hot there … Does anyone know what it is please ? Should I put new pads? there is no need to be replaced but maybe is the pad I don’t know the mechanic checked all discs pads don’t touch each other he told me is common sometimes can happened but when I press the break while driving the metallic scrabbling noise stops !!

what has happened to my little car ???

This could be the back plate on the front discs that is touching/rubbing, it could also be a sticking front caliper, it could even be the squealer that is fitted to one (or both) of the pads on each side to indicate they have worn down to the limit - but the mechanic said they were fine so unlikely the last option.

Good morning thank you so much for your replay will take the car back to the garage tomrw ,morning thank you again