Chain Noise I identified the problem, don't know how to solve it (chain/cassette?)
You may want to read up on how to tune a rear derailluer, but if you just want to get going, all that is needed is a minor adjustment using the barrel screw (clearly seen in the video) where the cable comes in. Turn the screw clockwise 1/4 turn at a time, and the chain will move away from the cog (The cassette is the full set of cogs). Trick is not to make big adjustments - no more than 1/4 turn at a time, and count the turns so you can go back to where you started. 

Once this is just clearing and not catching, check the gears are all working properly. Sometimes, especially with cheaper bikes and old worn out gears, its not possible to get it perfect, and you need to compromise a bit.