I would look at how your equipment is tied to the electrical grid. Odds are it is leakage from the AC line to chassis to interconnect shields. If you have one power cord it won't matter but if you have two it is guaranteed you have a ground loop. Have a power cord with three prongs and you have a bigger ground loop. UL is great for not getting shocked but they are very unkind to high end audio - their excessive leakage limits really screw things up.
Trying to fix hum leakage with shielding is expensive and marginal at best. The reason is you are treating symptoms and not the cause. The beat approach is to separate the transformer from the electronics physically with distance but if the transformer is internal, that isn't possible. Distance cures the hum radiation field, but there should be very little radiation with a torridal transformer.
You might try a medical grade isolation transformer between the wall outlet and your system, then make sure all earth grounds tie to one spot and only one spot. If you have equipment with two prong power cords, connect a ground wire from the chassis to the common earth ground. That will cure the leakage problem.