This "joke" is so old, I remember hearing it on "The Golden Girls." And I'm sure it wasn't new then.
I just looked on YouTube, and I found this 15-second clip, which unaccountably, ridiculously cuts off before the punch line (??) (Why anyone posted this, I have no idea.) But you can be 100% sure the cut off line is that the audience screamed "she's in the attic."