sounds like cans dragging under the car

I have a 95 Crown Victoria and when I crank it up since last night it makes a loud rattling noise that sounds like cans dragging under the car but it don't shake or anything what could this be

Last night I cranked it up and the rattling started and it got louder as I drove it when I got up to speed it went away a little and when I slow down or com to a stop it gets louder my heat or ac don't work ?