I'm making a separate thread, because otherwise this will just be buried and missed. A Ranger from Vegas was doing some minor things to my car yesterday, and when he was done, I asked him about the drivetrain issue. He said there is no issue. A while back they replaced a few for customers that were complaining of noise, and the Tesla engineers wanted to use that as an opportunity to look at them. I don't remember the exact wording he used, but he basically said there hasn't been a need to do any in a while. He said the gears are spinning fast, and they will make some noise at high speed. You will hear them because there is no engine to cover that noise.
I personally have noticed that if I don't have the trunk cover/liner on in the back, or the rear seats are folded down, I will hear the motor/inverter/gears at high speed. With the trunk cover on, I don't notice it. There is no way they are going to be completely silent. I think part of what has happened is that a few people posted about their replacements on the forum, and a bunch of other people started listening and then wanted theirs replaced as well, thinking it was a good idea. I think Tesla was very happy to have volunteers who wanted their cars taken apart and a new drivetrain put in for minimal noise, so they could look at how the drivetrains were doing in the real world. Personally, I'm not going to have my car taken apart for no good reason. Obviously, this is different from the very few people that have developed a clunk when coming off the accelerator due to a rare gearbox problem.
So my thoughts are:
1) Parts moving at high speed are going to make some noise, and you will hear it since there isn't a loud ICE to cover the noise. It is normal and will change over time as parts break-in.
2) You will hear the noise less if you use a trunk cover and have the rear seats up.
3) This is not a reason to not buy the car or worry about the company, as a very busy service center claims they aren't doing many, if any, at this time.