It rattles when I I hit the gas and when I put it n reverse.but it goes away on 1998 Plymouth Breeze

When I am driving and speed up I hear a rattleing sound and today for the frist time I put it n reverse and I heard a rattleing sound then it went away.

Asked by for the 1998 Plymouth Breeze
Most likely the cat. conv. is breaking up inside. Engine off, tap it with a rubber hammer to see if rattle is heard.