Definitly sounds like something is binding in your steering linkage, causing the servo to strain trying to center (giving you the buzz). Does the 7.5 come with a built in servo saver? If so these can easily be over tightened when they are installed on most cars, often the bushings they come have some flashing left on them from the molds that can make them a tight fit. To help find where its binding pop the tie rods off at the inside and turn the wheel to see if it still binds (the wheel/tire of the car, not the transmitter). If so then look towards your hub carrier, if not, its probably in your rack and/or servo saver unit.

If your car doesnt have a built in servo saver (pretty sure it does though) and you're using an aftermarket unit that attaches to the servo directly ensure that it doesnt rub on things like the servo mount, braces, etc..