1997 dodge dakota bad brake sensor?

hi..i have a 1997 dakota...when i hit around 40 mph...it use to be onlywhen hot..but now..seems to be around 140 degrees it starts...wheni put my foot on the brake...its fine...itssilent...but when im going down the road...it grinds...almostlike a bent rotor...but it has new rotors and new front pads....the rear axle is a new one...bearings arefine...it sounds like the pads arehitting the rotor when im driving....if so...wheres thesensor at?....no lights are comingon....any ideas?..thanks God Bless---Nick