Could possibly be a worn wheel bearing, best way to test for this is to jack the drivers side front wheel free of the ground, place a hand top and bottom of the wheel. Push the top away from you and pull the bottom toward you. If you get any movement, it likely the wheel bearings are worn. It could also be a brake cylinder seized, as I had a car come in a few weeks ago with a similar problem, caused the pad to always be in contact with the disc. Best to get that checked out at a garage. All the best, Chris