Possibly engine/transmission mounts. Or worst case scenario it’s driveshaft related like worn flex discs/u-joint. I’m assuming he replaced the transmission fluid and it’s at the correct level?
If you’re on a budget it might be worth adding transmission fluid additive and seeing if that helps anything.
Possibly driveshaft related
Probably worth doing especially if it’s a 4 cylinder (easier/cheaper) if it’s a coil and they’re easy to access then pull each one and look for and hairline cracks/splits on them and or oil to help pinpoint a specific one. Another thing to try is with the engine running spray a bit of water around each coil and see if there’s a change in engine noise.
1,100$ for a new engine? That’s a steal