Stuttering over 1/2 Throttle, no CEL: 03 MAN-SPI 2.0

The car stutters when you give it over about 1/2 gas. Fully stock engine. Noise sounding like metal rubbing corresponding with vehicle speed. I'm thinking low trans oil... I don't think the two issues are related. Where should I start looking for further clues about both problems? BTW this'll be my first of many posts Thanks!
--Darius