Robert
For temporary listening test only!!!!! Remove and then replace after testing the front panel and door assembly and take a listen to the improvement. I plan on having the machine shop I use that makes my brass parts for string instruments fabricate a hinged all-brass cover assembly. I think the magnetic fields generated within the box are disturbed by the ferrous cover plate. These newly bent magnetic fields are reflected back into the same box and become a part of the power signal that travels to your components and elsewhere, Ideally an entirely new box and cover plate should be constructed and installed by a licensed professional. That would be a serious mod and undertaking. TomD