My alpine single cd playing head unit has a very annoying click at about 1hz or so that happens only when I play a cd as opposed to the radio. This happens on new,old,recorded cds, it doesn't matter. I thought it was the unit until I tried playing a new cd on my computer and could also hear a faint clicking in the background. In the car, if I give the the dash a good slap near the radio I can change the clicking from bad to not so bad but eventually it returns.