a pulsating throbbing sensation...
For those of you who love playing the "name that noise game," here's a fun one. At 55mph +/- mine has a vibration. Its slight, nothing to get me too concerned, but noticable. It also pulsates. Say on a 2 second interval. the vibration seems to start at the front of the car, then progress toward the back, then start over again.
I must add, this is an incredibly dangerous situation. The gentle vibration and rythmic pulsation is very relaxing. Like having one of those massage seats in the car. Dangerous cause it'll probably lul me right to sleep one of these days!
(hey, can someone make a car crash emoticon?)