744TI 1987 with M46 box +o/drive. When decelerating in 2nd and 3rd gear I get a rubbing like a warped brake rotor type noise. It seems to be same frequency in both gears when road speed is same ie; propshaft speed I think. One opinion is overdrive rear bearings. Anyone got an alternative idea that doesn`t mean pulling the box. It doesn`t happen in top gear presumably because there is less torque.

I don't know what your problem is, but the mainshaft does not rotate relative the the input shaft in fourth gear, and the countershaft is not under load. You lack of noise in fourth would indicate a problem related to these areas.