ASM G-2 making odd sounds

[sinkingbeach]

ASM G-2 sounds like the sound of one drinking from a straw at the bottom of a empty cup, it's skimming as it always has but the sound just popped up. Both the skimmer and sedra pump are approx 14 months old. Any ideas as to why this sound would pop up out of the blue, the fix?

Thank you