Help! Reverse Whining. NOT normal. 06 AT

Hey guys,
I have been reading and reading posts/threads/etc. searching for an answer and no luck. I have a 2006 AT with 129k miles. I have had a lot of recent problems and have spent more time jacking with my car lately than I prefer (including a new front bumper, headlights, fog lights, skid plate, splash guards.) But now I have a problem I can't diagnose and I am afraid to take it to a mechanic because it could be transmission related.

So when I start the car and shift into reverse I hear a loud, clearly not normal whinning sound. I have read the threads where people think the typical reverse noise sounds concerning but it turns out the car is FWD and has different gears for reverse, etc. This is not that issue.

My car just started making this noise 2 weeks ago and the noise would happen occassionally when starting the car and shifting into reverse. Now it happens 100% of the time.

As soon as you shift into Drive the sounds dissappears.

Any advice? I am going to take the rear wheels off tonight to check the brakes but I have heard the sound of rear brakes going out and this is NOT that sound. Assuming it is the rear gear in my transmission....is there a DIY fix for this? Or am I in over my head? How much would something like this cost? Keep in mind the car is only worth around $8.5K on a good day with no mechanical issues.

Help! Please!

Trey (WHK3)
in Houston