HIGH PITCHED NOISE THAT INCREASES WITH ACCELERATION

(HELP PLEASE ) I'm New to this forum but, this our 7th prius. (Prius Enthusiasts!) My problem is a 2010 (our favorite year so far and the 4th of this model year we've owned.) We recently had a transmission flush at the AutoNation Toyota dealership. They did 2 of our 3. One started slipping gears within less than 2 months, we sold it.
Now one month later, our 2nd 2010 Prius started having a HIGH PITCHED NOISE THAT INCREASES WITH ACCELERATION and is quiet when not driving. The Noise seems to be center right behind the front seats.
HAS ANYONE HAD THIS ISSUE AND WHAT DID IT TURN OUT TO BE? We took it to another Toyota dealership (the best in the area). After a week, they pinpointed the noise and said it is coming from a specific point in the transmission, probably a bearing. Recommendation, drive it until it dies, or replace it but no guarantees. We live on a mountain and climb almost 1,500 ft in 4 miles. This is a fun car to drive up and down a mountain and we've driven it hard. We thought it could take it. That is part of the dilemma. Right now a good used tranny is really cheap in my area. It is also a very difficult time of year to sell a used older Prius. So.... What would you all recommend? And we've just put a bunch of money into it for expensive tires, all new fluids and tuneup.
If anyone has experineced this noise? Was it the Transmission? Or? Did you Wait and See? How long did your Prius run before it required repair?
Don't know if we should put the money to fix the potential problem, or wait and see? If we lived flat and didn't drive up and down a montain it would be a much easier choice. Appreciate your time, help, and advice. Thank you.

 

She has 163k highway miles. Not a lot of city driving, just highway. She's so tight that's why I invested in fresh fluids, top of the line tires. etc. Has everything I need.

 

You are absolutely right. Never again! And I'll tell everyone I see about it.
A former service manager told me the (coolant flush) and the transmission flush 'Machine' toyota uses is essential for the long life of the car. So I went to the dealership to have it done. (the relationship is contentious for years). The tech just hired told me he drained and then filled and I should probably keep an eye on the level in a week. What? One Drain and one fill, that doesn't clean anything. The ex service guy told the machine was the only proper way to flush, so I told the manager to send it back and do it again.
I was there over 5 hours. Maybe I pissed them off again, and they turbo blasted my transmission with the machine. (on a seperate issue, now they've forbid me from buying another car from them again! They use permaplate on all vehicles when they come in. Then they want to sell 'a warranty and apply the protection', without being up front that the product is on the car already. Now it is defective, causing problems to my Leather interior because the exterior product got on the interior and I have no way to remove the damage. But since 'I declined coverage' for a product I wasn't informed was on my car, no one will help me. Not the Dealership, not Toyota Corporate which said an application of an aftermarket product voids their warranty and that it is between me and the dealership, not even PermaPlate will help. So I Filed a complaint with the BBB for PermaPlate and they probably contacted the dealership. Now I'm banned from the dealership after buying 4 Toyotas from them! )
Question remains..... replace or ride til it dies and then deal with it? (right now I can get a tranny w 30k miles for $500! and they gave me a hybrid loaner! I got the labor cost down to 1,400, down from 2k. No Local Tranny shop can touch the bottom line.
So what to do? Thank you!

 

Thank you very much! only when moving and the higher the speed the higher and the louder the noise. Great question if the noise is there during EV, It's been at the dealership for so long now I've actually forgotten.