Two drums and a cymbal fall off a cliff
Two drums and a cymbal fall off a cliff... Da-Dum Tish
This is a meta-joke. This joke makes fun of jokes that end with the jokester making the noise of two drum beats and then a cymbal (which is sometimes called a rim-shot). Jokes that end in that manner often have a weak punchline, and this joke doesn't have a traditional punchline at all.
I suppose that if two drums and a cymbal really fell off a cliff in the correct manner they could make that noise, however this joke is not really that funny.