Phono stage hum at midpoint on volume control.

With the SME? How many ground connections on that table/arm. If motor and arm are both grounded and have continuity between them or if there’s no ground connection to either than that might be it.

Just starting with the obvious.

It’s a Clearaudio tracer tonearm. 
 

Wi-Fi router nearby?

@hiendmmoe 

-You list two different turntables in your components list. Which one is giving you the hum problem (or are both)?

-Does the hum increase in volume as you increase the volume level?

-I'm assuming you're not playing any vinyl when hearing the hum, correct?

-Is this something you're just noticing, or have you made some recent changes (cables, phono stage, etc.), and are now hearing hum?