Moving coil cartridge (AT OC-9) and Hum

I have 2 systems, the first uses an SME/Thorens with Supex MC cartridge into a Accuphase C-200 pre-amp. The second uses an OriginLive modified RB250/Revolver turntable with an AT OC-9 MC cartridge into a Carver CT3 preamp. Both systems use electronic cross-overs to feed multi-amp speaker systems. I have a Marshal Leach designed battery powered pre-preamp that when used on the first system produced no audible hum. Moving this pre-preamp to the second system however produced hum. The second pre-preamp is an older Dayton-Wright version that seems meticulously made and has a outboard remote power supply. It however produces hum on both systems albeit quite a bit less on the first system than on the second. The battery powered unit has much less hum on the second system than the Dayton Wright but the level is still unaccepatable. The hum is only audible while switched to phono on both systems. Is the OC-9 cartridge the culprit or is it the Carver CT-3 that makes the second system so prone to hum? I suppose I should switch turnatbles. The second system was only recently upgraded and with a MM cartridge, the hum was nonexistant, so I am very suspicious of the OC-9. Has anyone had experience with hum on MC cartridges (in particular the Audi-Technica OC-9) and can offer remedies?
i'd try switching the 'tables, if ya haven't done it yet. mite also try a s/s pre-preamp - aren't yours tubed? while i like toobs, they can be noisy on fono-stages w/low-output cartridges...

doug s.

What about the connection and dressing of the headshell leads? Another thought is degaussing the cartridge. Just "thinking out loud." Good Luck.
I have solved the "hum" problem and I do feel stupid. But hopefully others will not have to repeat my angst. I did switch out turntables and it was when switching back that the source of the hum became evident. The "Revolver" has a 3 prong AC plug and when you plug it in the "hum" starts and if you unplug it the "hum" stops. Use a cheater plug (2 prong) with it and the hum stops. Case closed. What a dope! Watch out for those 3 prong plugs!