I have a 1992 Infiniti M30 convertible with 46,000 miles on it. I am trying to diagnose and solve a vibration problem I have that comes and goes. I experience it primarily as a vibration through the steering wheel at various speeds, it feels somewhat like a tire that is unbalanced, scalped or with a bad belt. Sometimes it is more intense than others, and sometimes I don't feel it at all, thinking it has gone away, and then a few miles later it reappears. It is not intense enough to make the car unsafe or undriveable, it is just annoying as hell. The car is in excellent condition and has brand new radial tires that are in perfect balance. The car does not pull left or right on a straight road, so I don't think it is a front end alignment issue; I am thinking it could be bad ball joints or some other front end problem, but don't know for sure. Thanks for any help you may offer.