Salt shaker noise

I'm hearing what sounds like a salt shaker or a maraca from under the driver's side of the engine. It has a sh-sh-shhh sh-sh-shh sh-sh-shhh rhythm to it at idle and speeds up to just a constant salt shaker noise when cruising. Pretty loud; I can hear the sound with the window down when I drive near curbs or walls. I first noticed it about a year and a half ago but it went away after a day or two. Now it seems like it's there almost every other day. Car is completely stock, about 128k miles. Had an oil change last weekend, 5w30. Still pulls hard and has no detectable power loss or surging over the last two years that I've owned it.
Any ideas what the noise is?
mine is at the connection from the headers to the y pipe, i know you said yours is all stock but the end of your manifolds may be a good place to start at least, or around the cats
def smoke test it
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I'm not sure what the oil shop would be able to do. I heard the noise about a year and a half ago but it went away after two or three days and hadn't heard it again until about three weeks ago - before the oil change and after, no discernible difference. I'm not a gear head by any means, but if I actually had a hole in the block with a rod coming out wouldn't there be a huge noticible problem other than the salt shaker noise? Like a dead motor or a noticible decrease in performance??
I am hoping it's an exhaust leak. From what you other guys are saying, it definitely sounds like it. I also had my pops take a gander at it and he thinks it's an exhaust leak, as well. I haven't had the opportunity to get under the car yet (I'm a big guy and these bastards are LOOOOW) but I did happen to notice a pretty good dent in the I-pipe...battle wounds from encounters with speed bumps, I'm guessing. Would a good bang from bottoming out on a speed bump possibly cause a crack in the pipe/headers?
On a side note: The sound goes away after the car completely warms up. Not when the thermo reads warmed up, mind you, but maybe five or six minutes after the engine temps are up to where they need to be. Could this also indicate that it's related to the exhaust? I think I read somewhere that when all the exhaust parts are warmed up the metal expands and essentially seals off the leak if it's a small gap between the manifold and the header...does that sound like a reasonable assumption?
It WAS an exhaust leak. Where? I dunno... I just replaced the stock exhaust with some long tubes and an ORY and the sound is gone. Also had some backfire issues and other weird bogging issues that have all disappeared with the new exhaust. I must have had one beast of a leak if it was causing all those issues... I'm guessing the leak was right around the manifold/cat if it was causing the backfire and bog issues since that's where the o2 sensors were.






LMAO 



