Lexus Repair: LS400 vibration, radius arm bushings, radius arm

Question
Hello Zak, This ls400 has 120k. I purchased the car last July and at the time the radius arm bushings were shot and so replaced. Before replacement potholes could be felt strongly through body. After recieving car a vibration started to show up around 1500rpm to about 2300. Its a brmmm-brmmm-brmmm sort of vib not continuous and at a harmonic rate. It feels like it from the tranny tunnel, but can be felt in hands too. It has gotten worse over these last few months. It is strong when accelerating. There is a vibration in the motor when in park at the same rpms but I'm not convinced there are not more than one problems. The vibration certainly feels like a rotating mass, but tranny guys have said it doen't feel like torque converter problem. The plugs and wirers are original as far as I know, there is a slight exhaust leak. This seems to be a tough one, any suggestions. Thanks

Answer
Hello Scott, Well if the plugs and wires are original they are about 60k miles over due. Have you had the timing belt done? Vibration may be coming from something like motor and trans mounts to possible drive shaft problems or even tires. That is where I would start checking.