GenVibe - Community for Pontiac Vibe Enthusiasts

I have an 03 with 140k miles that has been great to us. A week a go my wife said that when she turned on the car it started to vibrate pretty hard. She then turned it off and on again and no vibration. It happen to her twice and it just happened to me. It vibrates steadily. Hard enough to feel it throughout the car. I then turned it off waited for a few seconds and turned it on again. Everything seemed well again. I forgot to check rpm's but no check engine code yet.Any ideas to what this might be? Sensors I should look at.

Quick update: This only happens when the a/c is on. It happened again, I turned off the a/c and the shaking stopped. Turned it on again and the shaking was gone. ???

My first guess would be that it is normal. My Vibe experiences some vibration when I first start it up and turn the AC on.