This is weird - I have an Intel 2.4GHz core 2 duo iMac 24" , and my wife has a new alum. Macbook. I get a repetitive dinging tone which I discovered seems to only sound when Safari is running and docked and I am using whatever other program. My wife has experienced this on her brand new MacBook as well, though not as often as I get on the iMac. Both machines are running OSX 10.5.6 with all the latest software updates.
Any ideas?