high pitched sound coming from driver side rear wheel well
 

so i drove over a road debris and stopped to check if i had a flat. a constant whining high pitched sound like from an old flourescent or neon bulbs was comiing from under the driver side rear. i checked under other wheels, but no such sound. is my transfer case going bad or what could this be? thanks in advance.

whine in left rear
 

Don't know what year or mileage on your ML. When I had my 00 430 I had the same problem. It was the fuel regulator of all things, which is part of the filter assy, in the LR fenderwell. There is an upgraded model out and my dealer replaced mine under my starmark warranty. Problem went away. Since sold it and bought a 05 ML500SE which is even better yet.

its a 2002 with 53k miles. is this something that needs to be addressed right away because i dont notice any performance difference?

LR whine
 

I don't know if it ever will fail or cause you a problem. You may have to ask Gilley about that if he's still on the forum. I drove mine about 5000 miles with it noisey and finally had it fixed when I found out there was an upgraded unit available. All I know is that when the sound of a machine changes, something changed in the machine, maybe a problem, maybe not!