I also have a ratteling noise, EXACTLY like Rebel. It is not lifter tick, which can be fixed with heavier oil (or new lifters). You can check that by listening closely to the front valve cover, If it's lifter tick it'll sound like they're beating their way out.
I have determined it has something to do with a belt. I'd like to say it's a tension pulley for the power steering or alt. But I really think it's the timing belt (SCARY!). I removed my top covers to check, and I see it wobbling, especially after I rev it. It seems like one side of the engine is moving faster than the other, creating slack. I would much rather say F*** THAT, since I put it on myself, and I know that if anything it's too tight...Which of course leads me to think, maybe it is too tight, so it somehow damaged the pulley on the water pump, causing the noise and the slack....
There's some of my random thoughts, Let me know if you think of something else.