something rattling under hood or dash under load

[vardenafil]

i have a noise that i cant seem to find where it coming from. if truck is idling it sounds normal. if i give it a little gas once the rpms jump over 2000 rpms? it starts to rattle real loud. it almost sounds like its coming from under the dash but there is nothing there except for the ac plumbing but the ac compressor is not hooked up. the belt is disconnected under the hood to the ac unit. what would cause a real loud rattle under load at operating rpms? is this timing related? i dont know what pinging or knocking sounds like.