Have a question on problem with my XL7 my mechanic can't find on 2007 Suzuki XL-7

When starting out the car makes a pull/tug action while building up speed. Off and on I hear a grinding sound. When car is at full speed this tugging seems to stop. When speed is reduced the tugging and grinding starts. My mechanic says he cannot find a thing wrong.

Asked by for the 2007 Suzuki XL-7
if a spark plug is cracked this would happen, It happened to me on a 1998 buick regal, same thing car would buck on acceleration but would cruise just fine...other than that I would look at either the mass airflow sensor or throttle body control....