MG Car Repair: third gear noise when accelerating, transmission gearbox, pitched whine

Question
Hello Howard,

I have a 1979 Midget with the 1500cc engine and transmission.  When I shift into third gear and accelerate, there is a high-pitched whine coming from the transmission/gearbox area as if a gear is loose or misaligned.  The noise only happens when I accelerate, with no power applied or decelerating it sounds normal.  1st, 2nd, and 4th gear seem fine.  I can only assume I'm looking at a transmission/gearbox rebuild at this point -- just wanted to see if you might have any pointers.

Answer
Hi Fred,
If you have oil in the box there is nothing you can do outside of the gearbox and the only way you will know exactly what is wrong is to take the gearbox apart to see. Just before you remove the box check the mainshaft nut (if it is not an overdrive trans.)
Howard