Vintage Simmons Drums (UK) Users Group

HI,
I'm the proud owner of an early SDS3, BUT ...
Got a problem with it, on every channels when I push the Noise /tone 
button to the extreme right(tone), I've got some sound which stops, 
if I come back down after 2 o'clock (?) on the pot , to the noise 
side...
Does any one can help or have any schematics ???
Please advise.
Patrice.