Problem with my HK 825 Preamp

Hey all!

This is my first time posting here. My current setup is a Technics SL 5200, and a Harman HK 825 + HK 870.
Everything was sounding great until I heard this clicking/crackling sound today. Thought it was coming from the speakers but it was coming from the HK 825. Unplugged everything and it's still there (Getting worse maybe?) 

So this is a sound from the preamp itself with no speakers connected. Any idea what could be causing this and how I could go about diagnosing it?

https://drive.google.com/file/d/1Fs4Jk0iYqeRyhRvD-E-gx_tSgavk3Y5p/view?usp=sharing