As can see also Ch3 noise rise when it is adjusted to bottom in your image where Ch2 have much more noise.
For not mess with things before basics have checked.
Have you done self calibration?
It need do so that it is power on least half hour if it have been in around constant room temperature. If it have been just before power on very cold place this time need rise up to hour but in southern EU this is not case. In some northern countries it may be, yes I have tested it in Finland.
After it is fully warmed and reached internal temperature equilibrium (minimum 30min) start self calibration and leave it run untouched. Before self calibration, and this is mandatory, all input BNC need be open, nothing must be connected to these. Also environment must not have very high EMI during self cal, least not near input BNC.
This may affect or not but it need know it is done and it is done perfectly.
Now if this do not change situation and ch2 is stil worst and ch3 also some clearly more fat trace than 1 and 4 it need look more.
First default scope and turn all channels on. (1us div, 1V/div, probe multiplier 1x, DC coupled and so on... just as default is)
Just as your images first is. All channels separately visible very near center.
Take screen shot 1
Keep CH1 and CH4 so that they are near center but bit different so that can see both separately.
Turn CH2 near top so that whole trace is visible.
Turn CH3 near bottom so that whole trace is visible.
Take screen shot 2
Keep CH1 and CH4 so that they are near center but bit different so that can see both separately.
Change CH2 to near bottom and Ch3 near top (just opposite as previous)
Take screen shot 3
Keep all untouched but now turn Ch1 and Ch 4 off. So that samplerate is then 1GSa/s
Take screen shot 4
Change CH2 to near top and Ch3 near bottom (just opposite as previous)
Take screen shot 5
Change Ch2 and Ch3 near center both separately visible.
Take screen shot 6.
If there is clear sign that Ch2 and/or Ch3 have same kind of situation what was in your previous message images it have some hardware problem. There is so many possible reasons that speculations and testing this and that, tests after tests are waste of time. This is not normal (if it is carefully and right self cal) Depending dealer perhaps you can ask they change it. If they do not accept but your return without reason time window is still open just return.
But these what I ask test may tell tiny bit more what is perhaps going on there. If you do not want do these tests, just make sure sefcal is well and right made and if situation is still as your images then it have some but rare HW problem. There can be small effect but your CH2 noise when it is moved to bottom is so bad I have never seen in this model.