Hi,
A while back I asked you to put a temporary (very short) ground in between the attenuator output and the amplifier input to find where the ripple is picked up.
I'm not sure if I saw feedback on this, I was busy, so I could have missed this.
If you have this temporary ground in place and the ripple is still there and is still the same, it is save to say the ripple is picked up in the amplifier.
If it is gone, it should come from the attenuators.
One other thought:
In one of your pictures it looks like there are two traces.
When you see this signal, can you play a bit with the trigger hold-off to see if that makes a difference?
Good luck,
Leo
satbeginner