Ever since the cold weather (and ice) arrived, My '91 Sportrak after half a mile or so of driving while decelerating will make a noise similar to a car with no exhaust at all (thats the only thing i can compare it to because the engine noise increases rapidly.) and will also rattle like hell, this will last about 3-4 seconds. Then there is a massive thud noise and it will continue running normally again.

I have no idea what may be causing this but it only happens on very cold days so does anyone know?