RFI from steel TV bracket?


Yesterday I installed a new TV on a steel wall-mounted extendable bracket between all my electronic components.
I now have a low hum/buzz from both speakers on all sources....even with the preamp on mute?
When I switch the preamp off.....the hum is still there.
The only way to remove the hum is to switch the amps off?
I tried grounding the steel bracket to the preamp and then the amps without success.
The previous TV was in the same location but sitting on the shelf.....not a steel wall bracket.
Any help would be dearly appreciated?
128x128halcro
Received the Cardas Clear XLR interconnects today and installed them between the Halcro DM10 pre and the DM58 monoblocks.
Absolutely no hum or buzz whatsoever.
The shielding in these cables is obviously so superior to the old Hexlink 5 interconnects and/or the balanced XLR method of connection combine to lower the noise floor from the speakers to nil :^)
Now I need time to see if I can 'hear' other benefits?