As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - FLIGHT 2503. ON TAXI RECEIVED A GLD UNSAFE MESSAGE. RETURNED TO THE GATE. MAINTENANCE PLACED THE RADIO ALTIMETER SYSTEM ON MEL 34-41-1. AIRCRAFT RETURNED TO SERVICE. MAINTENANCE REPLACED THE CAPTAIN'S RADIO ALTIMETER R/T. OPERATIONAL CHECKS GOOD. MEL CLEARED AND AIRCRAFT RETURNED TO SERVICE.