button under the hood

This just seems odd but in the top right corner under my (91 PA) hood is a button that isn't described in my owners manual or Haynes. If you press it it makes a loud rattling sound somewhere in front of the engine !
What is this, an air compressor of some sort ?

Can you post a pic of this button?

it's the round button on the right of the cable/hose going to the hood. I pressed it again, the sound comes from the engine, is it the starter motor?

http://www.uploadgeek.com/uploads456/1/27102008.jpg (http://www.uploadgeek.com)

Thanks for the pic, that button is defiantly not OE! It looks like someone put a remote start button there for some reason. :dunno: Can you trace where the wires from the button go?

Maybe it has something to do with the alarm? There is an aftermarket alarm built in, but I haven't had time to figure out how it exactly works.
Now I think of it, the sound seems awfully loud for the starter engine. It is really odd. I'll try to trace those wires later...