Cleaned my tt today, wheels as well. I noticed the inside tread of the rear tires were pretty worn out. I have about 25k to 30k of miles on them. I'd expect them to be worn, however, just the inside...
as a general rule, the wear on all 4 tires should be even .... if both rear tires show irregular wear, there is an issue .... most likely an issue with the axle .... if the wear has been from day one and it has taken so many miles to show, the issue is probably minor .... that isn't to say it shouldn't be addressed .... if it is a recent development, something must have changed and you need to find out what that is