The calipers could be starting to sieze, that is, not to release when you take your foot off the brake. This happens with age, quicker if you park overnight on dirt, or grass. To check, take the wheel off and use a pair of water pump pliers to retrack the pad/piston back into the caliper. This should move back very easily with one hand on the pliers. The more effort it takes to retract the piston the more the pad is likely to drag on the rotor. I have had calipers be free for ten years on a Volvo parked in the garage and seize in as little as 18 months on Volvo parked on damp surfaces like dirt.
Steve M.