60 Hz Hum

I just finished the http://www.aussieamplifiers.com N-channel, and it has a hum. I measured it with a hz meter and it is 60hz.
When I short the input it stops humming. Not sure if that means anything but that is how we tracked down ground loops in car audio. The pre amp is a Adcom GTP-600. It does not hum when connected to the GFA-5500. I tried unhooking the chassis ground but that didn't stop it. Any ideas on how to stop it?

Thanks in advance,
The hum could be due to your power supply layout. I found that using separate rectifiers for the positive and negative supply rails helps to minimize the chances of a loop. Each secondary winding should feed a bridge rectifier, which are then connected to the power supply capacitors. The ground point should be made at the capacitors and all ground leads connected at this point. +/- Connections should also be made at the capacitor terminals not at the rectifiers.

Hope this helps.
Thank you all for your help. I found the cause of the hum. Believe it or not it wasn't the amp. It was my X-10 signal bridge in my main breaker panel. It was on the same circiut that the amp was plugged into. When I changed plugs the hum stopped. So I plugged the amp back in and moved the X-10 to another ciruit. Now my amp works fine and so does my home automation system.