When I start my engine after it's been off for awhile, something in the engine squeaks like crazy.

I've opened the hood, and it looks like it's coming from the belt/chain on the side of the engine block. More specifically, it looks like the belt tightener (?) arm (an arm with a pulley that seems to serve no purpose but to keep the belt tight) is sliding back and forth, making the squeak against the engine block.

Any help?

 

So, I finally got my car to the dealer. They said that "there is an oil leak leaking onto the belt, causing the squeak." They've ordered a replacement part, so hopefully it gets fixed.

I'm just hoping they didn't confuse my spilling oil last time I changed the oil (which was about 5 months ago). But anyway, hopefully it gets fixed, and I'm under warranty, so I don't care if they do have to order something.