Need Transmission help

[highvoltage0823]

Not too long ago, I purchased a 1969 VW Beetle that I've been trying to restore. When I got it, the transmission had gone bad, so I installed a new one that had been rebuilt by a reputable local VW mechanic. As soon as I put the transmission in, I noticed that it was EXTREMELY noisy, noisier than any other Volkswagen transmission I've heard. In neutral, it makes a strange grinding noise, sort of like metal-on-metal. When I'm driving, it makes a horrible noise that sounds like a bearing (sort of a grinding spinning noise), but only when I give it gas. I can have the motor running at 4000rpm in 4th gear with no noise other than the transmission itself (it's also extremely loud, like I said, but that might just be the straight-cut gears), but whenever I give it gas, at high OR low speed, it makes that horrendous bearing noise. I was thinking (hoping) this was my throwout bearing getting ready to die, since it makes noise in neutral as well (this is different from the strange bearing noise, which only appears under accelleration); if not the throwout bearing, what could this be? Do I just have a poorly built transmission, or is this something I can fix?

[MGBGT]

On your Beetle did you put gear oil in your tranny when you installed it??
If so then thats obviously not the prob. You said it has straight cut gears?? If you do those usually make noise but not a grinding type noise. If the problem is in the tranny step on the clutch if the noise goes away then the problem most def. is in your tranny if the noise is still there then it might me your throw out bearing. Because the throw out bearing is only engaged when you press on the cluthch pedal. So it should make noise only when you push on the pedal unless the bearing is totally falling apart. but by the sounds of it its your tranny. Hope this helps

[highvoltage0823]

The tranny only makes noise when the clutch is engaged (not stepped on the pedal) and when I'm giving it gas. I guess that rules out the possibility of the throwout bearing causing that particular problem. The tranny makes a totally SEPARATE noise when the motor's idling. If it's in neutral with the clutch engaged or disengaged, it makes this noise; at one point it went away with the clutch in, but now it doesn't go away at all. Looks like the throwout bearing might be at fault here, which leads me to believe (hope) it could be at fault with the first noise as well. This makes much more sense, considering the person who built the tranny had many years of experience.
Note: The tranny was completely empty when I got it; I put the gear oil in myself and recently checked it, so i know that's not at fault.