Low level constant Noise/Hash on the output

[chris2u]

It looks like there is some constant higher frequency hash or pulses on the FG's output..
Here is a pix of a 1KHz/0.1V square wave.



Same again but with a sine wave.



With signal level reduced to zero, the noise is still there.



With the FG turned off but still connected, all is well.



Have tried using a linear power supply and adding caps across C9 and C10. but to no avail.
I hadn't used the FG for a while, so not sure if the problem was always there.
Maybe something needs setting to default?
Any suggestions, Thanks!

[jye1]

This noise is normal. It came from the digital trimmer U4. We can't find easy way to remove the noises.