I am hearing an intermittent bell sound on my Mid-2010 Macbook Pro. It sounds like the cash register sound that Quicken makes when you enter a transaction. I just reloaded a new copy of Lion on a new HD, but still hear the sound. I ran a virus scan which claimed the computer is free of malware. Has anyone had this problem? I suspect its a hard to detect virus or software that is running in the background eating up resources.