I have a 1996 Merc Cougar xr7 with a possible automatic transmission problem. When the transmission is cold I seem to have a problem when in gear and stopped. At red lights or in stopped traffic, there is a "rumbling" or vibration from the transmission. If I pop into nuetral the car the noise and vibration stops and when I let off the break and accelerate there is no slippage, it will shift through all the gears correctly and the vibration stops, it only happens when I am at a complete stop. The problem will go away after driving for about 15-20 miles and the transmission has warmed up. ANY IDEAS?