Grain on Sony Z5U Footage

I'm confident this is a common question, but I'm not finding a lot of answers that pertain to my particular camera. I have a Sony Z5U camera that I use for my corporate job. The main issue I'm facing is grain on my footage. I've read and reread and the manual and read all the tips online. There's obviously something I'm missing because the footage still contains grain. Here are the camera settings I most often use:

HDV1080i
30p
0 to -9 gain
30-60 shutter speed
f/stops between 3.5 and 5

I'm hoping someone on this forum knows this model of camera well enough to tell me what I'm doing wrong. I have a feeling there's something fundamental that I'm missing, or simply a camera setting that I have yet to adjust. Thank you in advance!

-Marty