all the standard issue mac software, plus firefox, and microsoft office for mac. Usually nobody is doing ANYTHING when it occurs. I'm sitting in the next room just now, and nobody is even using the imac, and it just made the noise! So, I guess the answer is, it occurs at random. I was wondering if he had some "alert" thing turned on, but I cannot find any setting to make it stop - - -esp. since we have to wait around for it to happen (If we knew how to make it happen, I guess, we would do better at stopped it!)
thanks for your suggestions on the temporary account/user. I will look into that.