My daughter'* 2000 Pont. Bonneville VIN K, has a whine only when the tranny kicks down into Overdrive. The sound goes away when you accerlate from Overdiver or if you shift into 3rd gear. I have changed the fluid and filter and used Lucas Auto Tranny....... Everything else seems to shift smoothly except for the annoying sound when in Overdrive. Looking for an answer..thanks.

Overdrive is fourth gear.......chances are, a bearing may be on it'* way out, in the fourth gear mechanical circuit.....

Did you notice any metal, excess clutch material in the pan during the filter change?

I always thought Torque converter lockup was considered OD. Huh.

I had always understood OD to be the terminoligy given for any gear that causes the transmission to have a higher output speed than input speed. Transmissions of old liked to max at a 1:1 ratio back in the old days if memory serves (direct drive?) and then put a friggin tall FDR to drive cruising engine speed down.

No metal or pieces in pan when doing the fluid/filter change.

Is it possible to safely record the noise by chance?

In third gear the input and output shafts are spinning at the same speed......in fourth, or overdrive, the output is spinning faster than the input.....the torque converter lockup is there to reduce the slip of the fluid coupling in third and fourth gears.....

Not knowing the loudness of the whine: Is it possible the whine is there in 3rd but covered by the extra engine noise?

Following this potential theory: If you're driving in overdrive and hearing the whine and the situation is safe to do so: let foot off gas and pop it in Neutral. What does the whine do?