Well if the Pixie doesn't hum with your antenna system but the Cricket does, that points to a problem on the Cricket somewhere ( they are supposed to chirp not hum [lol]).
Seriously, there must be a connection that isn't properly terminated, especially to the ground plane of the board. For example, is the shield of the onboard antenna jack well soldered to the board ground? So, what I would suggest is to go back over all the soldered connections with a hot soldering iron, just to remelt each. Sometimes you can push and prod at components with an non-conductive "tool" to identify the culprit. My favorite tool is a bamboo skewer.
I have built a lot of electronics scratchbuilt and kits, from pixies up to a K2. Nearly every problem encountered was due to poor or missing solder connection. Missing a connection with the soldering iron has happened many times. I even once encountered a connection with no solder on a 55 year-old Drake R4 receiver while troubleshooting an intermittent receive problem, the factory had evidently missed it.
Repairing a malfunctioning radio is one of the most satisfying aspects of this hobby.