What was found
IN CRUISE, FL430, AN AIR NOISE HEARD, FEELING A PRESSURE BUMP, & NOTED CABIN ALTITUDE FLUCTUATING BETWEEN -600FPM AND +400FPM. LASTED APPROX 4 MINS & LEVELED OFF AT 0. AFTER 10 MINS FLUCTUATIONS AGAIN, NOT EXCEEDING -300FPM TO +150FPM. LASTED ABOUT 3 MINS, RETURNING TO NORMAL. HAPPENED 3 TIMES, NEVER GETTING WORSE THAN ORIG CYCLE. DURING FLUCTUATIONS, PRESS MODE SELECTOR, SELECTED TO MANUAL, NO THRUST OR ALTITUDE CHANGES, FLUCTUATION STOPPED FOR 2.5 MINS. CREW RECEIVED A CABIN CLIMB RATE EXCEEDING 2500 FPM, & RAPID FLUCTUATIONS ONCE PRESS SELECTOR KNOB TO AUTO. R & R OUTFLOW VALVE ECMU CONTROLLER IAW AMM 21-31-01-000-801-A. R & R PRESSURE, A/CON CONTROL PANEL IAW AMM, 21-01-01-400-801-A. OP CHECKS GOOD.