Over here i have the same problem.
Tried a 4MS RP40 with 90W, a Pittsburgh EP-360 Case and a Doepfer Low Cost Case with PSU2.
Best so far was the Doepfer. But there is still a high frequency noise.
I bought also this “Noise Killer” adapter for the bus which have been mentioned in this thread. But they didn’t help at all.
The good thing is that i found a workaround for it.
Because this noise is the same on all outputs, you can mix together two outs while one of them has to be inverted. So the noise is cancelling itself.
With that workaround together with the Doepfer case i’m happy.