[Arran]

Sorry. I meant that when using the isolation transformer, grounding the chassis didn't seem to have as much effect. When running the radio straight from the wsll outlet, grounding the chassis helps a lot. I guess I'll have to run a wire from the GND screw on the back to a ground point somewhere in my place when I use it.

This is just a thought but have you tried piggy backing a pair of other caps across the line capacitors to increase the values? At least you figured out that it was power line noise and not something like a wire routed in the wrong place or an open ground connection.
Regards
Arran