Trigger stick and a "sucking" sound?

[Virtual Oyster]

Yesterday, I was playing with my stock classic mag on C02. I pulled the trigger, and the trigget stuck for a second, and the mag made a "sucking" noise. This happened twice. Is this a symptom of a problem that causes imminent doom to the marker, or just what happens when it gets cold? (Stupid Indiana weather) Any help/feedback is appreciated.

[Yama]

i think its because ur using co2 and ur valve might be starting to freeze up

[Cha0tic]

are you getting bolt stick and a leak down the barrel? try getting a powertube spacer kit.