My bet would be with Joe P. Either the fan/shroud clearance or the radiator/fan clearance.
When you changed the motor mounts, did you adjust the fan shroud to fan blade clearance all around? Tip of blade to top of shroud should be approx 20 mm, bottom should be 15 mm, and both sides (left and right) should be about even. Also, the clearance between the radiator and blades should be 20 mm.
Look closely to see if there has been any contact, all the way around pn the shroud, and on the radiator.