I have a 2006 Five Hundred SE with 160,700ish miles. Car runs great and i love it. However, when I'm accelerating there's a grinding type of vibration that I can feel through the gas pedal. If I press harder on the gas pedal it gets less, but it's always there for the most part. Its more noticeable when it's cold out and the car is warming up. Somebody told me front end, another engine, another throttle body.. has anybody else had this issue and what's the solution? Thanks!

 

Sounds like driveline to me.I would believe it would only be throttle body related if the roughness occurs only while you move the gas pedal.