noise when accelerating, but nothing when parked

[grouchman]

I have 2007 Nissan Maxima SE it has about 31k miles on it. when I accelerate I hear a rattling (like sheet metal), at around 2k-3k rpms. But when I have the car in park and accelerate the car I hear no noise. I went under the car there's nothing loose. the only modification i did to the car is put a HID kit on. Very puzzled right now.

[maxhopper]

Did you check all the exhaust heat shields?

[grouchman]

Yes, I checked all the heat shields around the exhaust but nothing seemed loose.