Noisy output stage?

[hylaster]

Is anyone familiar with his symptom: A filter, once connected to my PSU, develops a very pronounced hiss at the output stage. The level of hiss is independent of the input signal volume. The filter still functions other than this noise. The filter in question is a Doepfer A-106-1, but I have had the same problems with a couple of Synthesizers.com diode ladders (which I realize aren't designed to operate on +-12 but this shouldn't be the issue, right?) There is a 101-2 and a Bananalogue Serge VCS on the same bus that seem to be fine.

I am running my system on a Power One supply, +/12v 1 amp. Today I checked out the supply and the bus board and all the rails are delivering what they are supposed to.

Thanks!
chuck