Both of those things, the auditory and the visual, could be being caused by a process running in the background. Have a look in your login items for anything that could be the culprit. If that tells you nothing launch Activity Monitor (probably in /Applications/Utilities); set it to show All Processes, click on the "%CPU" tab (perhaps twice to bring CPU users to the top) and see what you can spot - you would be looking for something showing some CPU usage, possibly intermittently.
...and, BTW, it isn't a virus - Macs don't go in for that sort of thing! 🙂