[Elecraft] ferrites for subwoofer: before or after isolation transformers?

[Nicklas Johnson]

The backstory as briefly as I can make it: I wanted to place my home
theater subwoofer in the corner of our living room; doing so required
running two speaker wires and a coaxial cable under the house and plugging
the subwoofer into a different outlet than the AV receiver; this in turn
resulted in ground-loop hum (because of a tiny difference in potential
between the two outlets) which I worked around with a set of 1:1
low-frequency audio isolation transformers.  The subwoofer is of a type
that produces a signal based not only on the LFE channel, but also on the
left and right speaker channels, thus the two speaker wires along with the
coaxial cable.

Now the subwoofer is picking up common mode noise on 20m, which isn't
terribly surprising, as this happens a good bit with consumer-grade
electronics. I'm hoping to mitigate this with some substantial ferrite
clamps for all three connections and as many turns as I can get through
them.

My hunch is that the best place in the path to clamp them on will be
immediately before the connection to the speaker itself, on the speaker
side of the isolation transformer, but I wanted to get the opinions of
folks who have solved this problem in the past to see if there's any reason
the ferrites should come before the isolation transformers.

Thoughts?

   Nick

-- 
*N6OL*
Saying something doesn't make it true.  Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.