Easy now Dan...
Firstly, WELCOME to the forum and lots of good info from the folks here!
The whine is pretty normal and can be worse under heavy load, gear selection, going uphill, full bucket etc. It is hydraulic connection & not a direct response to throttle input.
They take a bit of getting used to with seat time & working the pedal/tredle, but can be abrupt if you come off fast (thus the easing off point).
Any other details? Is the tractor new or used (how many hours), when does it happen, how cold, ambient temp or warm-up time etc.