I have a 2003 Infiniti I35 with 180,000 miles. A few days ago I felt and heard some vibration coming from the engine. I turned the heater off to listen for it and the vibration stopped. Turned it on, vibration started again. Aha! I thought. Blower motor. I removed the blower motor and hooked it up and turned it on, holding it by the base. I was surprised that it ran very smoothly. I disconnected it and left the blower motor out until I could pick up a replacement. Out of curiosity tonight, I turned the heat on (with the blower motor still detached) to see if I might get some heat through the vents while I drove. I didn't heat, but the vibration started again. I opened the hood and noticed the radiator was vibrating a lot when the heater (sans blower motor) was on, but not at all when off. Any ideas?