B777 Captain reports interference; apparently from an AM commercial radio station; that hinders with ground crew/flight crew communications on pushback in SEA.

Narrative

On pushback and in the alley aft of gate xx there is excessive interference with the communications between the pilots and the ground man. I have tracked this problem over 6+ months and found it consistent. At the gate; communications are fine; but when in the alley there is interference. The intensity varies from just noticeable to such that communications with the ground man are nearly impossible. It occurs on all 777's that I have flown over the last many months; and is also heard by the other pilots. I have asked the ground man to hold down the mike without saying anything in order to identify the source. I can not positively identify it; but it is definitely a commercial radio station; and is a 'talk' station (not music). On one Sunday; I believe that a football game was being broadcast. That leads me to suspect that it was KIRO AM710. With the short duration available to listen; I can not further identify the station; and sometimes the dialogue isn't clear. This problem may be being ignored by other crews because we can usually hear through it. But not always. In that this definitely interferes with my communications with the ground man at a critical time (setting brakes; starting engines; releasing him from the headset) I consider it a hazard. I would be curious as to whether this also affects other types of airplanes in that spot; and whether it affects other airlines; who also push to that spot.