Engine rattling sound

When I start up my car I have a sound coming from up under the hood that's like a rattling like something is loose. It is not knocking as more of a rattling or ticking sound. When I accelerate it it stops. When I stop at a red light and it's just an idle it starts making the then rattling noise again like something's loose. The check engine light just came on but it stays on for just a little bit and goes off. It's not blinking the car doesn't run hot. I just bought it a few months ago and they said the clutch I just been replaced. It just sounds like something is loose or it may be hitting up against something like that piece of plastic or a fan belt hitting against a piece of plastic. But when I give it gas that noise watch down. You have any idea what this could be?