Buzz,
Do you notice it more when you're using the tractor in high gear? What HST range are you spending most of your time operating in?
I'm almost always in Medium range on my HST. Sometimes I'm in Low if I'm pushing into dirt or gravel piles with my FEL bucket, or mowing up a steep hill with the 3pt mower. I will also use High range when I'm running down the road in front of the house, going from the shop building to the main driveway.
With mine, in Low range, I don't think there's any whine at all. In Medium range there is very little, unless I'm loading it down, pushing the forward pedal down quickly and not letting the engine speed catch up (I have linked pedals). But in High range, I get a bunch of whine, especially starting forwards, or going up a hill. If I'm roading my tractor down a hill, the whine disappears almost completely.
Try operating in lower gears, start out in Low and putt around, see what the noise level does. Then try Medium for the same. As I said, I'm almost never in High when I'm working it, mostly in Medium. Also see if running your hand throttle up to 2000-2500 rpms does for you. Does it make the whine quiet down?
I had a buddy that was using High range on his compact almost exclusively for everything and was complaining about whine. When he switched to Low and Medium, his whine was greatly diminished.
