I have a 2015 L3901 HST with 287 hours on it. The tractor makes a whining noise when accelerating. The whine stops when the tractor is up to speed with no load on it. The whine is loud enough that it drowns out the engine noise. There is no whine when operating the backhoe or loader. All filters and fluids have been replaced with no change. There was no sign of metal in the oil. I bought this tractor used with 86 hours on it, and the tractor has made the tractor has made this noise since I have owned it. I was thinking it could be a relief valve passing, but not sure. Any ideas?