What was found
DURING CLIMB OUT APPROX FL230 ACFT EXPERIENCED A LOUD POP WHICH SEEMED COME FROM BELOW COCKPIT IN E/E BAY. A MOMENTARY CLIMB INDICATED IN CAVING RATE OF CLIMB TO 700 FPM THEN RETURNED TO 300 FPM. SOUND OF AIR RUSHING THROUGH COCKPIT CONSTANT AFTER INITIAL POP. A SECOND POP OCCURRED APPROX 5 MINS LATER AT FL 280. OPENING AVIONICS FLOOR ACCESS THERE WAS A DEFINITE INCREASE IN A NOISE. NO SUCTION OR DIFFICULTY OPENING FLOOR ACCESS. LVL 1 AVIONICS FAN OVERRIDE ON & AS LVL 1 CABIN INFLOW LOW. RETURNED TO MEM. FOUND AVIONICS COMPARTMENT DOOR SEAL MISSING FORWARD SIDE. REPLACED SEAL IAW AMM 52-00-00-4.