If it's been damaged from different sized tires, it'll make noise and often when making a sharp turn such as doing tight 180 degree turns in a parking lot. It can also make noise driving it normally but only if severely damaged and if so, it's usually then so overheated that it's also leaking fluid, burning on the front exhaust pipe (nice huh?).

There is no drain plug from the factory so if you want the fluid changed, I'd advise having a dealer do it following the info in the TSB or TNN.

To do it, one lower case bolt is removed, then one drills through alluminum into the case until going into the fluid. One then needs to flush out the alluminum shavings, then re-fill the unit with a specified amount of a special type fluid (not just 75W gear lube).
The plug you're seeing is the filler plug and that's that, nothing else.