Why do beds creak during sex?

I can ALWAYS hear my neighbors having sex – either their springs creak rhythmically or the bed is actually banging into the wall. But I’ve never made noise….at least not that way. I’m starting to think I“m actually doing something wrong, since everyone else seems to physically move their bed. The ferocity and speed of the kinds of movement that would make my bed sound like that just seem painful to me. What’s going on here?