I hear what reminds me of a very very faint drum beat coming from the computer tower. These faint "drum beats" occur approximately every 5 or 6 seconds sometimes the "beats" are closer together and at times a short period when there is none. This will occur when I am doing nothing on the computer except having an open window such as the one I typed this message in. I am concerned if something is running in the background or if this is normal. All replies will be greatly appreciated.