"Remove Hardware Safely" icon flickers off and on

I am having an intermittant problem. Ocassionally the "remove hardware safely" icon will flick on and off, accompanied by the "da dunk" sound. This will happen even when I do not have any external hardware connected. It will do this every few seconds or every couple of minutes.  I regularly use external speakers, a printer, wireless mouse and thumb drive, connected via USB, however this will occur when nothing is connected.  This does not present any functional problems, however the constant "da-dunk" while watching a movie or listening to music is annoying.  I have tried to determine what might be causing this by waiting and clicking on the icon when it breifly pops up, but the box that pops up to list the attached devices is empty.  Of course, there are no devices attached, but I don't know what else to do to figure out what is causing this.

This is an Inspiron 1525 running windows vista.