Phono Pre-amp Hum

Today I was listening to some vinyl and noticed that in between quiet passes, I was hearing a hum through my speakers.

I proceeded by powering off / on various components to see which one was causing this humming sound. I found out that it was the external phono pre-amp.

My external phono pre-amp is a Dynavector P-75 MKII which I'm using with the Dynavector DV-20X Low MC cartridge on a VPI Scoutmaster turntable. The rest of the system is all Linn.

Any idea why I'm getting this hum?