Grab yourself an action camera with either a super heavy duty magnetic mount or clean the surface of the area you intend to use the suction cup mount so the camera doesn't fall off. Now, place the tiny camera along with a decent led light in there with you so you can film the drive belt. You're interested in seeing if the drive belt is flopping around excessively causing it to hit the blades of the fan.
If you find this is the case, options are: Heavier tensioner spring (which more than likely will not resolve your problem) add an idler pulley to wrap the belt farther around the pulley that keeps failing. Also check to make sure the two pumps are lined up as closely as possible so the belt isn't trying to ride one side of the offending pulley.
Also, be sure to follow Bert's advice, he is the man.
