Jittery with local drive - need new HDMI?

I have a Shield Pro hooked up with my Samsung 75" TV

I have a number of flash drives plugged in via a USB extender port thing (i have 4 WD MyPassport 5tb drives and 3 SanDisk 512mb flash drives)

I occasionally get lagging with the picture and am wondering if it's because I just have too many hard drives plugged in or if i might just need a new HDMI cable and, if it's the latter, what's the best cable to get?