[TenTec] Jupiter display noise?

[Bill Fulling]

Howdy,
Recently my 3 yr old Jupe has developed an annoying rapid motorboating 
noise in the background audio.This noise starts at 18mhz and seems to 
peak at 21.357mhz.At first I thought it was external to the set,but it 
occurs in dummy load also.Depressing the menu button eliminates it 
completly and it can be made to occur while in menu by moving the tuning 
knob to highlite the menu items.The speed of this noise varies directly 
with knob speed.Returning to normal operation reinitiates the noise(sort 
of like "running rabbits"on a radar screen.)Anybody have any ideas 
what's causing this?
73 de Bill W4NJF