the fact that it doesnt make the noise in park leads me to believe it
is a rotational part of the drive chain.  in particular the cv joints
inner cv is the norm if it is under acceleration. if it is extremely
worn you will also get lost power.  the next part is the torque
converter system inside the transmission.   will rumble when loaded if
bearings are  gone.
jimt
On Thursday, Oct 17, 2002, at 14:00 America/Denver, Blake Heinlein
wrote:

> Hi Everyone,
>
> I've been working on a mysterious power loss for the last week or so.
> I
> have an '84 Westy Automatic 1.9L Digijet Injection.
>
> Here are they symptoms:
> - Idles fine
> - Accelerates at about 1/2 of normal rate
> - Makes a deep muffled roar when accelerating with load.  This is a new
> noise that I can't explain.  Sounds like I paid a lot of money for a
> new
> muffler.
> - Can't imitate noise while in Park.  If I rev the engine in park it
> doesn't make the noise.