[morzh]

Check how you dressed the wires. If you decided to bundle some of them - unbundle them and try in general to avoid running wires in parallel for long distance.
If any were run next to the chassis before, keep them this way.

an idea: while having the screeching sound, try to move wires by touching them with an insulated rod of some sort, see if at some point when you touch some wires it disappears. This will give you and idea if there are some proxymities between some wires that should be avoided.