What the heck is wrong with my ht??!!?

[Lt. Aldo Raine]

slim ps3 hooked up to sony strg 720 by hdmi...

ive been having problems with my system for the past while
everytime i watch a movie there is crackling or something in the speakers, not all the time just at certain parts, not in all the speakers at the same time, like one part it will be the right, then the left, then a rear, then center
and its with almost every movie,
and it dosent happen randomly, if i replay the part it happens again, and again
i dont understand what is going on?! i kno its not spose to be like this
is it a receiver problem? i have a entry level receiver sony 720, could it just be the quality of that?
ps3 problem? cable problem?
im really confused and upset, i spend all the money i have on my ht, and im not happy with it, i wonder why i spend money in the first place
i was planning on saving up and buying a new receiver, cuz i think that mite be the problem, but how do i kno for sure before buying?
how do i solve what the problem without spending more money?

i dont kno how to explain it, any questions feel free to ask
any help would be appreciated