Symptoms of crank pulley being broken?

[JTaylor2005]

I have a rattly sort of noise in my engine. I have heard that sometimes the crank pulley can rattle and cause it to sound rough. I also notice when I let off suddenly I get a really quick short rattle as well.
Do you think this could be the crank pulley on its way out? What else would I notice if anything on that issue?

Thanks, Jack