Not sure if this is the right place to post.
98 western star with 3406e cat.
noticing a kind of “rattle” under the cab, only when accelerating and only noticeable over 40 km per hour.
U joints all good steady bearing okay, sounds and feels like it’s in the area of the tranny. Letting off throttle makes the “rattle” disappear. But it will always rattle regardless of how much I’m pressing down on the throttle. Any theories?