My 2015 Grom has a vibration that I’m not sure where it’s coming from. The vibration increases with RPMs, not really the mph. You don’t feel it in the steering wheel but in your butt and knees when snug on the bike. It has 950 miles. Mnnthbx intake, dual underbody exhaust and fender eliminatator/LED tail light. The mods have been on for quite a while and I don’t think they are the cause. I changed the oil around 500 miles with the Honda synthetic oil. What should I check next?