Hearing it again I would say its more open looped amp motorboating. Cant
analyse for frequency etc until tomorrow. Needless to say have not been able
to induce any noise like this.

Further info from the owner
" It's whenever there isn't a signal that the buzz persists. I first noticed
it when i stopped playing in the middle if a song and i heard this murmur"


140K MP3 , 5 second file, is (theoretically ) now on/off this host site
http://www.diverse.4mg.com/amp buzz.htm

(minimal htm page to get round "forbidden" remote linking stuff )