Keith,
Is this high frequency noise? Like in the 10's on MHz and above? If you like you could post a photo of the noise.
It is possible with an oscilloscope for the loop made between the probe tip and the earth clip connection to form a nice antenna, and it is possible that a different method of earthing makes a different length loop that is not sensitive to the same frequencies.
It sounds like the noisey load center must contain an inverter, or have a problem load that is generating noise. It would probably be good to work out what the noise is, and filter it out at the bench.
You can probably see it if you just hold the oscilloscope probe tip near the mains Active wire.
Richard