Reported as fuzzy sound on the bass guitar E string even at relatively low
levels
but otherwise fine sound rendition or backing off the bass control .
Feeding a signal generator in then indeed a distinctly fluttery distortion
in the range 50 to 70 Hz on top of the wanted output, ok above or below that
range.
No external speaker output on this cube and before getting inside to scope
it or run an external speaker I took the front grille of in case of
parasitic rattling but no change. But putting a sock in the front/back vent
tube in the speaker surround cured it.
Where to go from here ? sci.acoustics.repair ? charge for an old sock ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/