I think the weirdest part about this "inappropriate" laughter is that the same people are clapping at the end and coming back every week and probably talking about how great Hitchcock is.
Well, yes, inappropriate laughter is definitely annoying, but there's also an extent to which Hitchcock intended certain things to be funny.
I caught ROPE at The Charles a few weeks ago and there's no way that Hitchcock didn't intend more than a couple of those laughs. Until the emotionally heavy climax there's quite a lot of intended humor there. There's more than a little bit of camp in John Dall's performance. And given what he was implying about Brandon's relationship with Phillip it's not as though Hitchcock was being subtle.