possible 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.

Have you checked the wheel bearings, ball joints and other front suspension components?

No. I kind of got off on the drivetrain being the problem after doing a little research on it. I just don't know how to isolate it to one thing or the other. I'm taking the car back to shop that did the motor mounts tomorrow. Although it was an honest mistake it did not fix the problem I asked them to fix. I mean may be the motor mounts were "weak" but I would have rather had the noise fixed.