Just wanted to post my experience here in case anybody else finds it useful. I'll try to keep this updated with any further developments in the future! Feel free to PM me or reply to this if you have any questions or suggestions.
2013 Chevy Cruze LT with 1.4L Turbo & 6-speed Manual Transmission (M32) (currently with 54k miles)
Discovering the issue:
My girlfriend bought this car in Summer 2016 with around 34k miles from Paddock Chevy in Buffalo, NY. Paddock sold the car to its original owner, received it as a trade-in a couple years later and then re-sold it to my girlfriend, so they were familiar with the vehicle. Since buying it, she has driven about a 50/50 mix of around-town and highway driving. In mid-August of 2017, with around 53k miles, my girlfriend noticed that the transmission had begun making an abnormal whining noise in 5th and 6th gears. The noise could best be described as similar to the turbo whine, but somewhat lower-pitched. When the engine is at the same RPMs in gears 1-4, the noise does not exist, yet it does very distinctly in 5th and 6th at those same RPMs. This, in combination with the fact that the noise varied directly with acceleration (loud when accelerating, faint when coasting), led me to believe it was related to the transmission. We also noted that the noise only occurs when the transmission has warmed up to normal operating temperature (20 minutes of driving or so), and is most noticeable when between 40 and 55mph, due to the fact that above 55mph, the road noise tends to partially drown out the whining. After doing some googling, I discovered the mega-thread on the M32 issues on this forum, as well as several UK sites describing their issues with the M32. The extremely common bearing failure issues described seemed to match the exact symptoms that we were experiencing. Because of when the vehicle was manufactured, I am very confident that the transmission was under-filled from the start and had never been filled to the correct level (since the transmission fluid has not been changed since the original purchase of the vehicle).
Solving the issue:
I made an appointment to take the car to Paddock to have the transmission checked. Before leaving the car, we took it out for a quick spin with the service advisor (Kyle) riding in the front passenger seat, and as soon as we got up to speed and shifted into 5th for the first time, he immediately acknowledged the whining. I also informed of the research I had done which indicated a bearing failure, and explained the exact steps & conditions necessary to replicate the issue. We then returned to the dealership and left the car, since it couldn't be looked at immediately (because apparently there is one specific mechanic at the dealership who specializes in this area and he was out that day). At this point in time, we did not receive a loaner vehicle, as they had not yet determined that the issue was covered under warranty.
Two days later, we received a call from Kyle, who informed us that after investigating the issue, they had determined that the transmission was eligible for replacement and would be covered completely by the powertrain warranty (of which we still had 9 months/46,000 miles remaining). He told us to come in and pick up a loaner whenever we were ready, so my girlfriend picked up a 2017 Trax later that afternoon. Paddock has ordered a new replacement transmission which should be in within a day or two, and will be installing it and should have the Cruze back to us within a few days. I will update once the replacement is complete and we have the car back!
At this point in time, it looks like Paddock has really stepped up to the plate and cares about making this right- they haven't tried to pretend the issue doesn't exist or tried to give us the run-around like other users on here have experienced. Kyle has been polite, understanding, thorough, and definitely deserves a raise. It might help that the dealer is familiar with the history of the vehicle (since it was purchased there twice), but from how they handled it, I suspect they would have taken care of this even if we had not purchased from them. I'll update down the road once we get the car back with a new transmission!
I'll also be taking it to my local small-town shop to have the trans fluid changed out with one of the heavier-duty fluids recommended in the megathread (after a couple of weeks to allow for some initial break-in, of course). I plan on doing this both so it's running with a higher-quality fluid, and so I can be certain that it is filled to the correct level (since I know the guys at the small shop well and can be sure they will fill it with as much of whatever fluid I request).