Stumped Troubleshooting Amp

I've completed a build of a LM3886 kit. It consists of the PowerZero Power Source power supply, with the upgrade to the 160VA transformer, and 2 point Zero LM3886 modules.

Here is the problem. If I power up the amp, with or without source connected, it will emit a loud, 60 hertz-ish buzz. Here is the strange part...this happens only around half of the time I fire it up. If I leave the amp alone, not changing any other conditions, it may or may not buzz.

Any ideas where to start on hunting down the gremlin?

is the hum from both channels?

check for loose connection/bad solder joints. you can do this by tapping/pushing on every component including input and output terminals. use something non conductive to do the pushing and speaker you don't care about. you can do this first without any power to check for any obvious loose connections.

make sure all your grounds come together at one point (star ground).

also, something as simple as taking the the ground for each channel from different points off the transformer center tap wire can create hum.

sorry i can't be more specific. as nuuk suggested some pictures would be helpful.