Honda atc 250sx. Transmission
 

Hi, so I hear a funny wining noise from the output gear case when the atc 250sx is in first gear only. It is pretty loud and definitely not normal as my other one and my big red sound fine. Any ideas if this could be a simple problem? The book shoes the entire engine being taken apart to change the gear case. This is the gear case that is at a 90 degree angle connecting the engine to the drive shaft....

Any help would be greatly appreciated!

Thanks