Need Help...Bad noise from under car

[Prater]

After racing to about 130, I developed a very high pitch whining noise coming from somewhere under the rear of my FRC. I can put the clutch in and rev the engine and there is no noise, but once I let out the clutch and give it some throttle I get that sound. It does not happen when I let off the throttle. I also do not get it in first or reverse gears. I can also feel slight vibration in my shifter when the sound arrives, and the pitch changes slightly when I shift, or move the shifter with the clutch disengaged. Any ideas?? Is this the syncros maybe, or is there any linkage that may be rubbing somewhere....Just hope its not the rearend. If it is the tranny, anyone have a M12 for sale at a good price. I will probably go with that tranny if there is extensive rebuilding to mine.
Thanks for any suggestions.