Transmission whine, but no issues other than sound

@vtgu2wu4it2nvc Any thoughts how long I can go ? That is so hard to predict. Since it is working a should and it's only whining, I think you are having the right plan by continuing to service the transmission exactly as should. The only other thing I would consider, is to take it to a place that specializes in transmissions. They are the experts on this and can and will check pressure etc. and can give you a much better prognosis on this.

You mentioned that Toyota has issued a bulletin (related to T-SB-0160-18) for certain 2017–2018 Highlanders. This was to address a condition where a washer tab, designed to prevent the loosening of a nut inside the affected transmissions, was not sufficiently bent during assembly.

Of course, this can cause the nut to loosen over time, leading to internal wear on components like the bearings or planetary gears, which produces a distinct high-pitched whining or grinding sound that increases with acceleration.

Here is the MC 10159729 ZJC UA80 Warranty Enh and I love this paragraph "Although the UA80 transmission equipped in the subject vehicles is covered by Toyota’s New Vehicle Limited Warranty for 5 years or 60,000 miles (whichever comes first), we at Toyota care about the customers’ ownership experience. Thus, Toyota is providing coverage for repairs related to damage to the UA80 transmission caused by the previously mentioned loose washer tab and resulting in the symptoms described above."

You may want to remind Toyota of this :-)