Diagnosis
The OEM polycarbonate sub-base is prone to cracking from overtightening or drops. This causes imbalance and vibration.
How to Fix It
Order the replacement sub-base, part #RYB311202. Remove the old one by unscrewing the four Phillips-head screws. Install the new base, hand-tighten the screws in a crisscross pattern. Do not overtighten.
If That Didn't Work
If vibration persists, the router's spindle or motor bearings may be damaged from running with the cracked base. You'll need to have the motor assembly checked.
Heads Up
A cracked base affects cut accuracy and is unsafe. Stop using it immediately. Aftermarket aluminum bases exist but may void warranty and require different screw lengths.