Gear Spinning Like Noise. Need Help Identifying!!!

[maclegend43]

My truck just got back from the transmission shop after having to rebuild my tranny and replace the transfer case,
now whenever I am cruising between 1500-1900rpms, it's make a terrible noise, almost as if gears are just spinning.
Also it will make a screeching noise whenever I place it in reverse but do not move. Naturally I take it back to the transmission shop, and they tell me that the tranny and transfer case are fine, and that it is probably my exhaust.
What do y'all think?
Any ideas of what it could be?

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It runs fine, it just makes the awful noise and I want to make it stop.

[RhinoZ24]

They're full of it. Exhaust doesn't do that when you change gears. You paid money, they should back up their work. Call their bluff and attempt to save money, take it back again.

[Jersey_Joe]

They're full of it. Exhaust doesn't do that when you change gears. You paid money, they should back up their work. Call their bluff and attempt to save money, take it back again.

X2^^^^^. That's horse ish. Take it back. No way it's your exhaust.

[maclegend43]

Was messing around under the truck and found my drivers side front cat shell to be coming off, I clamped it down and it seems to be sounding normal and no more rattling. Hopefully it stays quiet now and no more problems come up. Perhaps it really was the exhaust.