the low "pop" could be from a circut burning out.
do you smoke? is there alot of dust inside your pc?
i fried a memory stick from smoke scum.. the dust devils touched 2 points on a stick and arced. "snap" and smell of fried electric components. took about a day to find the melted contact on the ram stick, never though to look at that.
MB and processor were un-hurt from the issue, but PC wouldnt boot without memory.
just a suggestion.