As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING TAXI OUT THE YELLOW HYDRAULIC SYS WAS CONTINUOUSLY HAMMERING. CREW STOPPED TO CONFER WITH MOC AND WAS ADVISED TO RETURN TO GATE, DURING TAXI BACK TO GATE THE CREW RECEIVED EICAS OVERHEAT ON THE YELLOW HYD SYS AND CALLED FOR CFR SUPPORT. YELLOW SYSTEM, NR 2 ENGINE DRIVEN HYD PUMP REPLACED IAW AMM 29-13-51. COWLING CLOSE C/S 83661.