Voiceover Recording Issue

Hi Friends,

I've had a very frustrating recording issue lately.  I don't know what induces it but here's what happens (at random).  In my audio track, the noise floor noise (airflow, etc.) will rise and become louder as my voiceover becomes lower.  It's almost like the power of my signal chain is straining.  My noise floor goes from -50 to -40 and my voice just gets killed.  I'm using an Apollo Twin Solo with a 416 microphone.  Anyone ever experienced this?  It's very negatively affecting my business.

Thanks for your time!

-Tye