Lots of noise that looks periodically oscillating

[drnktank]

Hi,

I have assembled the DSO board and checked all voltages. Everything seems to be OK.
When I turn on the DSO the line appears to be oscillating more than what could be expected. This makes difficult to even impossible to look at signals. I have tried various power supplies and batteries. All times the same, so it is not a psu switching noise.
When I make contact between the two cables the noise seems to disappear.
A grounding issue?
Any possible solutions?
I will enclose some pictures of the noise.

[jye1]

Since sensitivity was set 5mV/div, the highest, the noises are likely the signals that the probe picks up in the air. This is normal as electromagnetic fields are everywhere. Please try setting the sensitivity lower and see.

[drnktank]

Unfortunately it is also at higher settings too. Please look at the pictures attached.
Can you recommend any test to run to the board?

[jye1]

These still look normal. As sensitivity was lowered the amplitude was also reduced. You saw a clean line when the clips are shorted. That indicated the noises are from outside of the scope. Have you tried the built-in test signal ?