As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE AT FL 340, AN ALTITUDE DISAGREE EICAS ILLUMINATED INTERMITTENTLY. CAPTAIN'S ALTIMETER READING 34,000 FT, FIRST OFFICER'S ALTIMETER READING 34,220 FT. ATC MSP NOTIFIED UNABLE TO RSVM. PERFORMED LOW LEVEL AND HIGH LEVEL LEAK CHECKS ON PITOT AND STATIC. REPLACED LEFT ADC.