To the best of my knowledge, battery noises are usually a byproduct of being charged. I have often heard those kinds of noises, and am usually not alarmed, but,... Next time, see if your battery feels hot, or at least overly warm...it may be being overcharged. do you have a voltage gauge? And have you checked the water in there lately? I know alot of batteries are "maintainance free", but if the cap can be pryed off, I'm there..peering inside with a critical eye.
(watch out for the acid that could splatter, also batteries release hydrogen gas...remember the Hindenburg?)
Hope this helps a little, I am sure there are people out there with more info...I just got here first, that's all.