Just a thought... You could have a tire with a break in the belting under the tread. In my pickup I had a tremor ongoing for a couple years. Finally it got bad enough I stopped by a Firestone shop in Billings. They found nothing. A few weeks later I went into a Les Schwab's North of Sandpoint, ID. The experienced fellow on duty found a worn-down-flat spot, a "bald" spot, on the tread about 4" to 5" in diameter. There was a break under the tread that allowed the tire to bulge un-noticeably, but the bulge in the tread caused a tremor and caused excessive road wear over the bulge to make a bald spot. Since I purchased these 6-ply tires new at Schwab's, the tire was replaced with a used, traded-in tire at no cost. Within a month the tremor returned and Schwab's in Reedsport, OR replaced another tire at no charge - same problem, a break under the tread causing a bald spot. After returning home to Hermiston, OR I had yet another tire replaced with a break under the tread and a bald spot. The Hermiston Schwab's, where I originally purchased the new set of four tires, wanted to charge me for the replacement tire. When I pointed out this was the third of the set of four tires that developed a break under the tread and the other two tires were replaced by other Schwab stores, then the employee immediately capitulated to no charge.
One thing I learned is if the wheel is removed from the vehicle and placed onto a spin-balance machine at a slow speed you can plainly see that a tire with a break is out-of-round. The tire kind of wobbles while spinning. Thus the vibration we feel. I would submit even if your tires are new, one tire can still be defective. I now have a new set of 10-ply Cooper tires from Big O in Yuma, AZ.
