People who laugh like rusty motel beds

My sister is one of them. When she has food in her mouth that is. Her laugh sounds like two people are getting it on in the next motel room, and I can hear it through the paper-thin, piss-stained walls.
One of the biology professors, same thing. Only difference is that he laughs at jokes he makes himself, that are not what you'd call funny.
Anyway, there's nothing wrong with these laughs, just not... en masse... There probably isn't even anything wrong with them, it's my problem. I hear those laughs and I can't help but think of fat, middle aged men with hairy arms wearing sweaty wife-beaters, going at it with cheap hookers sporting crack bugs around their mouths.

And you know, this whole thing is probably ridiculous, because most motels probably have nicer beds than the ones I imagine when my sister laughs.