[jmauz]

Hello, I have an MP512 unit that's several years old. It's worked flawlessly up until recently. When I turn on the lunchbox, the mic pre outputs random static, and tapping on the input transformer makes it worse. Eventually it goes away and all is well. 

I can't see any solder joint issues. Could the transformer be bad?

Thanks in advance for any help!

[JPK]

I don't believe the tranformer can become faulty. Try reflowing the solders.
Reinsert the DOA to make sure the connections are good.
Try tapping on the large caps to check if it increases the noise.
Also do the same on the pad potentiometer.