I have recently tried to use a Rode videomic pro with my nex 7. The mic is working and sound is being recorded however there is a constant undertone hiss. I have tried recording in diferent places, so it is not a background noise. I have tried the mic out on my Mac and it works fine, which makes me think it is to do with the nex 7. I have fiddled with all of the settings on the mic, and it makes the noise regardless. Does anyone have any ideas of what this could be and how to fix it?