What was found
AIRCRAFT LEVELED OFF FROM CRUISE CLIMB. ACFT WAS ALLOWED TO ACCELERATE TO CRUISE SPEED. POWER WAS SET TO CRUISE POWER SETTINGS OF 23/23 IN MP AND 2300/2300 RPM. FUEL FLOW WAS SET AT 12/12 GPH. APPROX 10 MINUES LATER, A SLIGHT JOLT WAS FELT WITH A CONTINUED SLIGHT ROUGHNESS. UNABLE TO DETERMINE WHICH ENGINE WAS AFFECTED (OR IF IT WAS AN ENGINE). TRIED TROUBLSHOOTING BY REDUCING MP ON LH ENGINE THEN THE RH ENGINE AND CHECKING THE MAG DROP. THERE WAS NO DECERNABLE CHANGE IN ROUGHNESS, OIL TEMP, OIL PRESS, CHT. NO VISIBLE SMOKE, OIL LEAK, OR COWL VIBRATION. CONTINUED FLIGHT WHILE MONITORING ENGINE GAGES, ROUGHNESS, ETC. DURING LANDING WITH REDUCED POWER, ROUGHNESS INCREASED. LANDED NORMALLY, NOTED RT RPM WAS 100 RPM HIGHER THAN LT ENGINE WITH BOTH THROTTLE CONTROLS PULLED TO IDLE.