I have a constant vibration, which is worse at lower RPMs (1500-2000). If I am coasting 35 mph in drive, then accelerate, the sideview mirrors flutter. Have taken into various shops for diagnosis, but all have given different explanations. Replaced fan clutch, harmonic balance, replaced joints in driveshaft. Also had engine tune-up and computer diagnostic test ran, which reported no problems at all. Don't know where else to turn...