Contour Enthusiasts Group Archives Forums General Troubleshooting Wiggle in 3rd

When accelerating hard in 3rd or 4th gear, I sense the slightest bit of vibration from the driver's seat. It's not a quick vibration, but more along the lines of a slight pulse every half second. i can't tell where it's coming from, but I feel it a little in the seat. Nothing shakes violently, and it is not felt in the steering wheel. It's so minute, that often I think it's my imagination. Any guesses? Thanks in advance.