>I suppose the new muffler could be more back pressure than the pevious
>like you guess. Now consider that low revs don't generate as much
>pressure out the exhaust. If you comine higher revs and the new
>muffler, it might explain why get the sound at higher revs but at low
>revs nothing sounds different than before. Takes both factors
>combined maybe.
>
>Then again...
>
It was the air tube. I clamped some aluminum foil over the end of the open tube to seal it, and the noise is gone !