Friend's car, a 2008 six speed manual with 130K miles. At RPMs between 1500 and 4000 there is a vibration felt in the pedals predominately the clutch pedal. The vibration is stronger in gear and while in motion. It can be felt at rest in gear with RPM at idle. The clutch was replaced 30K miles ago. The harmonic balancer was replaced a few months ago and currently shows no signs of wobble at idle and up to 3K RPM sitting in neutral. The car is a daily and is also auto crossed on the weekends. It runs fine but there is a vibration in the pedals most noticeably with the clutch pedal. If at cruise speed and barely depress the clutch pedal you get a foot massage. While shifting normally you get a strong vibration in the clutch pedal. My C6 is a 2006 with auto so I don't have anything to compare it to. His father has a 2013 GS with a six speed manual and his car does not have the vibration in the pedals. Any suggestions on what to check will be greatly appreciated. As I said the car runs and drives fine but he doesn't want to push a bad situation if there something major waiting to break. Thanks.

As an add to info, there is no vibration in the steering wheel, dash, or door panels. It's mostly isolated to the pedals and firewall area.

UPDATE: Found the motor mounts bad. Not quite broken yet but exceed limits.