TBM pilot reported the aircraft started to vibrate during climb in icing conditions. Pilot descended to warmer conditions which caused the propeller to sling off accumulated ice and the vibrations to stop.

Narrative

As I climbed to altitude in IMC I encountered light rime icing between FL200 and FL280 temps -5 to -22 C. Climb performance was decreased from use of the inertial separator. Deicing equipment was all turned on and working properly. Vibration of the airplane arose and was unexplained. I changed the propeller RPM and found the vibration to worsen. The CAS did not show any abnormality but because of the vibration it was decided that immediate descent and landing were appropriate. I [requested priority] and started a descent to ZZZ1 the nearest large airport. As I descended through VMC and warmer temperatures I saw the propeller sling ice off to the side and the vibration immediately disappeared. It was obvious to me what the cause and resolution to the vibrations were. The propeller had accumulated an unbalanced ice load causing the vibration. Once it had warmed the ice had melted off and the problem was resolved. I notified ATC via ZZZ Approach and asked to continue to original destination of ZZZ2. After landing I contacted my training CFI who confirmed that this was a normal procedure and information for future flights.