Grinding while in gear

[Video]

So this is new to me. I've herd of grinding while shifting into gear as a result of worn syncros. But I'm getting a humming/grinding noise while I'm already in gear. I havnt singled out any particular gears but I'll just be going along and I can hear this dull grind and I can feel it through the shifter knob. It lasts a couple seconds then goes away if I pull it out and push it back in or if I push it harder into gear. I'm gonna do a transmission flush tomorrow at work. Costs me like 10 bucks. Any ideas?