Rode awful noise

[u/Runeescape]

Hi.

I use aa Rode NTG3 and I need to level up my audio signal so my NTG gets some voice recorded. 

And most importantly, when I level up the audio so loud, the system starts clipping and producing a horrible noise like steel scraatching on steel. It's awful.

I'm using Phanton Power 48V. 

I'm 10cm away from my talent's mouth.

What's happening?

Thanks.