What Causes "Howling" Rear Gears?

Just about every part in a rear end has been listed here as a possibility.
I just took my car out tonight for the first time since swapping in an 8 1/4. It has 3:55 gears & a Trak Lok unit. I had a guy in town set it up for me that has been doing axles & transmissions for almost 50 years. He replaced every bearing, seal & race. He took the Trak Lok apart, inspected everything & reassembled it. Topped it all off with gear lube & sure grip additive. 2 different guys said that the ring & pinion looked fine. First trip down the road it sounded fine under acceleration but as soon as I took my foot off the gas it started to roar, howl, whine, whatever you want to call it.
My guy is telling me that it is the ring & pinion that are bad, he could hear it over the phone when I called him. Some research is pointing towards possibly being set up wrong.
Any advice? Where should I start? Second opinion maybe? Have I ruined it by driving it 2-3 miles? Any help is greatly appreciated. Funds have been drained this winter & spending $200 +/- for new gears & then more for set up again is not sounding good not to mention more than likely having to pull the rear end out to make everything easier. Thanks