Trans Noises

I currently have a 1997 K 1500, 350 with roughly 150k miles. I have no knowlage if the trany or engine have ever been rebuilt. Ive had a faint noise coming from the front of my transmision, that sounds like a water pump going out with the similar grinding noises before the water sprays. I was told by a local tranny shop that it was deffinetly the tranny without him even testdriving it. Then I asked a few people with limited experience with trannys and they told me it deffinelty wasnt the trans. The noise is not constant and it occurs in every gear, R-D-N-P. The trans dosn't slip or hardshift and it engages imidiently. To me it shows no sign of trans problem. Do you all have any advice what it might be and what could be loose. Thanks in advance for the help.

A whirring noise generally is the thrust bearing in the front of the transmission right behind the pump...Due to poor lubing.. You might get away with a fluid change and refill
However have it double checked by another shop, it could be somethign stupid like the alternator resonating noise to the under side of the truck.. Though its rare I have seen it

Thanks for the advice Ill have another shop look at it and give them an Idea what I think. If... I mean if... I was able to fix it myself it is a job that any joe could do? and if so is it pretty extensive, I understand dropping the tranny and all that good stuff but anything that needs special tools? Thanks for the advice again and Ill keep you tuned in.