I have a macbook pro 15in from 2009. Its hard-drive had to be replaced in 2011 and they upgraded the hard-drive for free and i believe it runs on snow leopard. for the last few months my mac has been "crackling." The sound doesn't appear to be coming from the speakers. It started out as just when it was starting up. It then became a problem during start up as well as during use. Sometimes when I start it up, lately more often than not, it will not start up the first time and has to be manually shut down and then restarted up again. when it refuses to start up it makes a loud, almost emergency-siren sound that is just a continuous beep. I have a feeling it is the harddrive again but it is a completely different set of "symptoms" than last time. I know there is a way to check if the harddrive is producing errors but I can't remember how but I'd like to do that before I take it in to apple. Anyone had this problem before?