I'm getting an intermittent grinding type sound from the front passenger side. It only makes the sound moving forward and it is much more noticeable at lower speeds, sound seems to be at same point for each wheel rotation. Up on stands the wheels turn fine, wheel bearing is solid, rotors aren't overly worn or warped, rotor guard not bent. I did find that one of the guide rods for the caliper was extremely difficult to move so I cleaned and lubed it and it moves freely but made no difference. Car recently passed an out of province inspection and also an inspection at a Chevy dealer while making the noise???!!! Any help much appreciated