Lawn Mower Issues

I have been having issues with the hydro gear 314-0510 transmission on my 4 yr old Husqvarana yth2148 riding mower. I was hoping someone could help me, basically got the mower this season and at first noticed one weird whining screechy noisy when backing up a hill didn't repeat. The next day my neighbor was using the mower to dethatch their lawn and it was constantly making this noise when under load no noises with no load unless driving fast and turning aggressively. The engine is fine and there is a momentary loss of power but is okay after words. Today however I has able to get it to whine up in place with no movement at all. Since the issue doesnt seem to happen during slow normal action I dont think the transmission is broke but that the drive belt is slipping. I however cannot figure out how to tension the belt. Anyone out there know how to tension the belt? Thanks jer
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