Rear derailleur hitting chainstay (video in the post)
Rear derailleur adjustment can be a really pain in the neck. What is more likely happening is that you have to adjust the B screw:


  B-Screw Adjustment After setting the L-screw, check the "B-screw" for
  an adequate setting. The B-screw controls the derailleur body angle,
  hence the name, B-screw.


You can find detailed information about all the setting for a rear derailleur here, including the screw (B-screw) that adjusts distance to the bike frame. You should adjust this AFTER the other two screws that adjust upper and lower limits relating to the cassette are properly adjusted, so follow ALL the steps one by one and you should be good.

It is also possible your derailleur hanger needs alignment. Watch your bike from behind and see if the body of the derailleur goes down parallel to the bike frame. If it doesn't, you need to adjust with a specific tool, so you should take your bike to a shop because it's not worth buying it. You can find more information about hanger adjustment here.

Good luck!