Whining noise from transmission boot

I have a 5sp, 99 Forester w/ 190K. It recently started to emit a whining noise from the shift boot area. The noise came on suddenly and not gradually. No changes have been felt or noticed in the cars overall performance. The fluid levels are all fine. The noise does not become noticable until 45+ mph. The clutch does not have any effect on the noise level, nor reving the engine. The noise seems to be related to the overall speed of the car. Could my installation of 18 inch rims a few weeks back have anything to do with this new noise? Anyone think my going from 15 to 18 inch rims screwed up my cars AWD/drivetrain?