My 2006 Prius has an intermittent chirp that sounds somewhat like tapping the horn softly. It appears often just after I turn on the power, when I stop at stop lights or in my carport, and sometimes after I turn off the power. Usually there is a single chirp, but there have been as many as 5 in a row. The dealer has no idea what it could be and it is intermittent so that it is difficult to track down. It has been present at least a couple years. I haven’t noticed this at highway speed, but that might be because road noise masks it. Any idea what this could be?
Click This Link And See If This Sounds Like It.
http://community.cartalk.com/posts/list/2129654.page
CSA