Here's the rundown, I downshifted from 5th to 2nd a few months back at about 75 mph. Nothing internally was damaged as far as the motor is concerned however the transmission has been making a high pitch whistling noise ONLY WHEN I ACCELERATE

1st Gear it makes no noise

2nd Gear at about 30mph it starts to become noticeable

3rd-5th Gear Anytime I hit the gas and accelerate it makes the noise, as soon as I let off the gas it stops.

Its most noticeable at exactly 58 mph in 5th gear.

I drained the fluid in the trans and the magnetic drain plug didn't have a crazy amount of shavings. Based on my searches it could be an main shaft or a countershaft. Any have a problem like this? I really want to take care of this ASAP.