This guy I know has a S4 n/a and he said that when he's driving down the road there is a grinding/droning noise, but no vibration, and when he takes a left hand turn quickly it goes away but when he turns right it's still there.

Could it be the Right Rear wheel bearing?

 

Sticking caliper maybe?

 

Good thought...anyone else?

 

Jack up the rear & check for wheel bearing & CV joint play (or noise).

 

I had the same thing like a week ago and to get a new caliper 500$$ from the dealer they installed it because I ahd no time and the idots didnt bleed the lines right so now I have to push the pedal to the floor to stop all the way (sorry for semi offtopic)