[CQ-Contest] AC noise

[Marco Spalluzzi]

Hi guys, I've got a problem, probably related to ground connections.
When I tx and my amp switches on tx, I hear a little ac noise in the
headphones, but it's not only there, it really goes out.
An US guy said it's little, but you can hear it if one listen carefully.
It's not a gnd problem of the headphones (Heil HC-4), since it's the same
with a desk microphone.

If the amp is on, but I disconnect the relay switch (so it doesn't switch to
tx), the noise disappears.
I replace the relay cable with another one (2 cables + shield), with one
cable connected to the cable shield.
Grounding this or not, nothing changes.

I grounded it through the gnd connector on the back panel of the 775.
Grounding it to the amp, or any other device, could change something? I
think no, ground is ground for everyone.

I made some "disconnect and try" tests, first with unused antennas (it's not
an rf problem, and in fact it didn't help), then with some computer cables,
pc ground, rotator cable, power supply ac cable, ... but I didn't solve it.
Should I connect "signal gnd" to "shield gnd" on each cable?
Or, if connected together, should I separate them?
I really don't know what else disconnect.
Could it be due by an excessive mic gain or compressor gain, or both?
Pse answers here on the reflector, or private to ik2xsl at amsat.org
Thanks in advance, bye Marco - IK2XSL.