Noisy rear derailleur (Shimano RD-5800) From the moment of buying the bike from a friend of mine, I have noticed that the rear derailleur was a little bit noisy. I thought that it would be problem solved by cleaning and greasing the jockey wheels.

Unfortunately, I have thoroughly cleaned the rear derailleur and sprayed some teflon lub on its surface. I have also removed and applied teflon grease on the jockey wheels, but the problem continues.

I have uploaded a video of the noise, and notice that it is an aligned chain situation (large chainring and 4th smallest cog). When I go to the 5th smallest cog, the sound gets worse.


                
            

This is a photo of the derailleur alignment in the same settings the video was taken:
Most of this is included in the comments...  I'd start with derailleur alignment.  Once that's done, you'll need to do some light tuning on the cable tension and limit screws to make up for any changes.  If that doesn't fix it, maybe a new chain would help.  Try borrowing a different wheel(with the same number of gears) to see if it still makes the noise, that will eliminate the cassette and hub body from possibly being the culprit.  I know you're saying it's coming from the derailleur, but it's sometimes difficult to tell when all these parts are so close together.  In the long run, though, if it's noisy, it may just be noisy.  If it's functioning right, it may not be worth messing with.