Rattling noise?

I have a 2000 Jetta VR6. Just recently it has started to make a rattling noise, like the kind of sound a big truck would make almost... As I drive off the frequency gets higher and then it stops around 40mph, now i'm not sure if thats because it gets drowned out by other sounds or if it actually stops. It seems like something might be loose, the sound is in the front... Does anyone know what might be causing this? Anymore info you might need? It's driving fine right now but it's starting to worry me... Let me know!

check you're transmissin or your muffler. just a suggestion. u didnt mention 5spd or automatic?

oh! automatic, sorry bout that. thx!

check the moter mounts