Ok first off the car has itr cams, aem cai, jdm 4-1, carsound cat, rsr exmag..

I actually have two problems, first off when the car is idling there's a loud rattling noise coming from the cat area of the exhaust, I put it on jackstands and tried to see if it was a heatshield or something, but it's not. The sound seems to be actually coming from inside the exhaust (although sometimes the way sounds get muffled around from the sound of an engine it's hard to tell). And once the throttle is over 1600 rpm's I never hear it. Also gets quieter the hotter the car is (less vibration being the reason I'm guessing).

Second problem. In the past few days I've noticed a few times that when I get into high revs I will see some greyish/black smoke come out of the exhaust accompanied by the engine faltering/dropping revs a bit. It then teeters back and forth for a half a second or so. This usual seems to be when I'm going up hill and the car is under a harder load (or turning).

Oh and about 4 weeks ago I did a valve adjustment, and changed the spark plugs. I'm pretty sure the car is running lean because the old spark plugs were pretty white.... planning on getting hondata or something for some tuning.

Thanks for any suggestions/advice.

-Nick