[1 Lucky Texan]

have you checked the front diff's fluid level? That dipstick is on the other side from the transmission DS. (US pass side - might be covered in grime)

If you lost some of that fluid, say - from a bad seal - the front differential could easily be under-lubricated and noisy. (though, it's odd that in neutral the noise stops - still, diff and transmission could behave differently under load)

The front diff can be repaired or replaced separately but that may be impractical compared ot the cost of an entire tranny/diff unit.

maybe someone here could suggest a different mechanic near you that has good subaru experience. This has the possibility of being expensive and second opinions are probably worth the time/$ to acquire.

 

[1 Lucky Texan]

have looked for a trans on Car-Part.com--Used Auto Parts Market ? sort your search by distance, shipping will add at least $150? if you have to ship, sort by price and see if you can find a deal.

FYI: used part prices in VA get higher the closer you get to richmond and DC.

yep^^^

and, some of the parts listed on ebay are possibly local to you if you're in a larger municipla area. A guy here at work just had his Ford 1.9 liter Escort drop a valve seat. He found rebuilt heads on ebay and one of the better prices is from a town just east of his home.