2000 LeSabre Limited Front End Vibration
 

Have a front end vibration present between 40-50. The vibration started a fe months ago. The tires were about shot so figured new ones were inling.It is present under acceleration and when on cruise control. Just had a brand new set of tires installed and had a 4-wheel alignment. I was about 3-4 miles from the tire place, accelerate to 50 and the vibration was still there. Went back to the tire dealer next day (about 12-13 mile round trip) and they found a weight off on the front. Replaced it and I departed. Same thing: few miles from dealer and got up to 50 with the vibration 40-50. Went back to dealer 3rd time. They recalibrated the balance machine, rechecked the alignment then drove the car.
They agree the vibration is still there! They are going to replace all 4 tires. The more I think about though, I doubt that will fix it as the vibration was there before the new tires and remains after installation. There is no clunking sound from the CVs, no noises when turning only the vibration/thumping between 40 and 50. HELP! Any suggestions?:)