I don't know about that Keith. It's meant to cure DC Offset which is likely reason for my humming 250DR. Mike at Airlink said it also lowers the noise floor.
We tried just about everything Chris. It's baffling. A different RCB and MCB made no difference. We didn't have another switch to try but will get one. Wire connections in back of socket we're checked secure and impedance is almost identical to that in the ring. We didn't check the wires in the two Henley-type junction boxes. Will do so. The idea about plastic CSU followed something I read elsewhere about plastic being better than metal related to Hifi but I suspect it's foo. And you're right - very hard to find a plastic one today. (My sparks said it's to do with containment of a fire in CSU and melting plastic dripping onto firemen.) Meantime we've left the radial on PME because I think it did improve things a little for whatever reason and it reduced the variables between the two in terms of process of elimination.
I thought the BPS would be worthwhile regardless of whether it ends up on ring or radial?