I feel there's a lot of excuses on this thread. I go to games at lots of levels, in lots of places. It looks fairly simple to me. A group of people, who have decided to make a constant noise in support of their team.
I know you get shot down - we don't want any of that at The Lane, etc.
But, for example, the Aberdeen fans, in a long winless streak, just sang constantly for the first 45. Because they'd decided that's what they were going to do.
In many football cultures there is no particular link between on field performance and crowd noise. Indeed, it's a badge of honour to just keep the noise up irrespective of what's going on.