FK10 FLC RECEIVED A GPWS TERRAIN WARNING DURING DEP. THEN DISCOVERED THAT THEY WERE OFF COURSE WHEN THE DEP CTLR QUERIED ABOUT THEIR RADIAL. TRACK DEV.

Narrative

DEPARTED YUL RWY 28; SID DORVAL 1. AIRBORNE; TOLD TO PROCEED DIRECT YUL VOR AND DURING TURN TOLD TO GO TO HDG OF 340 DEGS TO INTERCEPT RADIAL OUT OF YUL. WHILE FLYING 340 DEG HDG WE WERE IN MODERATE RAIN AND LIGHT MIXED ICING. THE RAIN MADE IT NOISY. OUT OF 7000 FT MSL IN CLB; RECEIVED 'TOO LOW TERRAIN; TOO LOW TERRAIN' AND THIS ALL ADDED TO THE WORKLOAD CONSIDERABLY. MISUNDERSTOOD INSTRUCTIONS AND THOUGHT WE WERE YUL DIRECT YXI. ATC ASKED OUR RADIAL OUTBOUND FROM YUL. WE STATED ACTUAL RADIAL AS 270 DEGS OR 280 DEGS. WE FELT DISTRACTED AT CRITICAL TIME DURING COMS WITH ATC. INCREASED NOISE LEVEL ADDED TO MISUNDERSTANDING OF CLRNC. SUPPLEMENTAL INFO FROM ACN 326071: TOLD TO PROCEED DIRECT YUL VOR R TURN. DURING TURN TOLD TO GO TO A HDG OF 340 DEGS TO INTERCEPT FLT PLAN RTE. FOR SOME REASON; MISUNDERSTOOD INSTRUCTIONS AND PROCEEDED DIRECT YXI AFTER YUL AS OPPOSED TO YUL 310 DEG RADIAL AND 70 DME; THEN DIRECT YXI. QUERIED BY ATC AS TO OUR HDG; GOT CLRNC RIGHT THIS TIME; INTERCEPTED YUL 310 DEG RADIAL TO 70 DME THEN DIRECT YXI. DID NOT APPEAR TO BE A PROB WITH ATC.