My friends, I've got a 66 long bed 250 six with a four speed "granny" trans... Two years ago I rebuilt the engine and it runs great... thanks to this site and advice from some great local mechanics. A few months ago it started to make a howling sound when ever I let off on the gas. Give it some gas and the sound immediately stops. Going down hill if not accelerating, it starts to howl again, going up hill with power, no noise. Is this a trans problem or drive train problem...? frankly the noise sounds right under the seat... any help with what it might be would be greatly appreciated.