Update on this, the sound is always present when on AC (using the FW 180 watt power supply and provided cable). It just gets louder when reading/writing data. On battery the laptop is nearly silent when idle but you can still hear the buzzing when reading or writing data (and you can tell the difference between reading and writing).
In a quiet room I can hear it up to about a 2-3 feet away before it gets drowned out by other humming things in my house. I have quite sensitive hearing.
I’m still assuming it’s probably normal.