vibration

[mountainman]

Just before leaving for parade I had new tires and a balance don on the 04 boxsterS. Noticed a vibration between 45 and 70 on the trip that is pretty noticeable, in fact it vibrates the driver's side mirror bad enough to make it distort the image of cars behind. My first thought was drivers side front tire as the mirror on the passengers side did not seem to be affected. However, I am starting to wonder if a front motor mount might do that. It has the original mount in it and it is time for a new one. My balancer is usually very good. Anyone able to shed light on a similar vibration?