I have a different tractor but I got the OEM Branson filter on line for about $25 at either Amazon or ebay. However, after SH the total was around $50. I don't have a dealer close by. I guess I could have called them and had it shipped. Probably would be the same money. I don't loose very much oil changing filters either. However, I get everything ready and the spin the old off and stab the new is pretty fast.
Mine has a little whine at the higher rpms. Below about 2400 it's quiet. I know it does it under load; don't remember it doing it unloaded. Very well could be just gears getting used to each other. I don't have any instability with any hydraulics including loader operation. I have had this tractor since 2007 and it is just now loosening up where things like shifting in/out 4wd is easy. It's rated hp is at 2500 but the factory set the pump up to 2700, I guess to ensure that tractors out the door meet the specs. It is very well built, that's for sure.
My first reaction to your post would be air in the system, but just changing the filter that should be minimal and you said unloaded, not loaded. Just don't know.
Mark