Rattling sound on Ford escape when accelerating
 

Hello everyone
On my wife's 2005 ford Escape there is rattling sound as if 2 pieces of metal are vibrating against each other. This happens when acelerating from a dead stop, and when the engine is cold. There is no sound while going in reverse, nor when it's in park and I step on the gas, nor when it's cruising. When everything warms up-nothing. It only happens when in drive and when accelerating from a dead stop.