Hi bro I would start with the wheels balancing, bearings check and alignment once you are satisfied with that and still have the issue. Then check chain ans sprocket alignment as well as wear on these items. Run a dial gauge over the rear and front wheel axles to check if its running true while you have the wheels off, axles you may wanna take it to an engineer to check on the lathe. Message me if this doesn't solve your problem. Ill try to help further. Note : These checks are for vibration whilst in motion.