This morning I noticed my 1982 245 making a metallic rattling sound when slowly letting go of the gas pedal to decrease speed. The noise seems to be coming from the rear undercarriage. I'm not sure if this noise has come up in the past, but it sounds like I heard it before. Later in the evening, I also realized that the noise would come on when I gas it. Sometimes it seems like the noise is coming from the passenger side of the undercarriage, near the cat. But the noise seems to mainly come from the rear. I can reproduce the noise in PARK and stepping on the gas. With the hood open, I can hear the noise near the fuel filter (on the driver side). The noise isn't like metal scraping or grinding; it's more like a rattling sound, like a loose metal washer vibrating against a metal surface. What could it be?