What is that high pitched whine that occurs when I accelerate or decelerate?

I just had my 2003 Honda Accord Ex in the shop. I was without my car for a week. I broke down on the highway and had to have it towed, not once but twice. I took it to a reputable Honda/Acura repair shop. It turns out the ECU was corroded and the A/C drain was plugged up. I was not aware of the design of the Honda in this area, however, with the A/C unit being above the ECU in makes it easy to destroy the ECU if there is any problem with the A/C. Seems to me that Honda might have wanted to recall this to put plastic between the 2 to prevent the corrosion of the ECU or something, however, no such luck. The mechanic pointed out that the carpet on the passenger side was damp and to check it. Who woulda thunk? I got the car back yesterday, after spending almost $900. Ouch. After running the diagnostic equipment they had to replace the ECU and ignition responders, put plastic between it and the A/C unit, replace the spark plugs (apparently the wrong ones were installed), and #4 coil, have the keys reprogrammed, replace the A/C filter and clean the A/C drain. Now here is the rub…I got it back and drove down the block. There was a high pitched whine or whistle sound that occurred when I accelerated. And the same sound when I took my foot off the petal as it was slowing down. I immediately drove back to the shop and the mechanic and I took a drive. He had heard it also before I got it back. He mentioned it might be the transmission and that if it needs replacing it may cost up to $3200. The car has 170,000 miles on it and it the past 2 months I have had new tires and this repair bill so I’ve spent over $1500 to date. He suggested I drive it over the long weekend (Labor Day) then make an appt to bring it in next week to have the transmission checked. Oh and I did I mention I’m not employed or a descendant of the Rockefellers? So here is my concern, if it is the transmission will I do more damage by driving it? Will it get worse quickly and break down thereby leaving me stranded again? What is the best thing to do? Any suggestions will be greatly appreciated. Thanks

Is your wife sitting next to you when this happens?

If you put it in neutral does the noise go away. Then it would be tranny. If not it could be any number of cheaper things, brakes, wheel bearing.