drivetrain problem

I have a 95 corolla with 150K miles that is making a hollow clunking noise when accelerating/decelerating. It has to be one of 3 things but so far after taking it to 2 shops and replacing motor mounts no solution found so far.

1) Motor Mounts - Been there, done that. Didn't fix the problem.
2) CV joints - good possibility but the boots are still intact and I'm not getting the clicking noise that everyone talks about. I do however get a shutter going up hills and braking at higher speeds (say >40 mph).
3) Differential - Haven't found much info on how to diagnose this one but I did read somewhere it could be causing the noise. Not even sure how to fix it if differential gears are the problem. Transaxle shifts normally.

Thanks for any insights.

Are you sure ALL the transmission and engine mounts were replaced?
I am not sure about your car, but other FWD cars have up to four below and one on top of the engine. Find them all and check them yourself. Don't rely on your mechanics word for it.