If you have a Manfrotto Magic Arm and it makes a horrible clunk & or grinding noise when you lock it in place then you have a problem, not an insolvable one, but a bit fiddly.
The problem seems to be a bearing that jumps out of its runner so it needs to be put back in its place.
You will need an allen key, you may need some grease as well, if it has been doing it a while there may be bits of ball bearing floating around, so you may also need a replacement bearing set. Which are available from our friends Manfrotto Spares in Dunsfold .
Firstly loosen off the silver allen bolt a couple of turns, this will free up the locking handle end so that the handle can be removed by unscrewing it. Make sure that you keep the assembly together in your hands as you will otherwise be hunting for the 9 ball bearings on the floor. Once the handle has been removed you will see the three seats for the bearings.
Simply place one bearing in each seat, and re-assemble, takes all of 5 minutes. Job done, no more grinding.
Good luck , as with most things, Don’t try it if you are not confident that you can manage it, as I shall not be answering individual requests for help (probably), and don’t try it if you are in the warranty period, also accept no responsibility for you getting bearings stuck up your nose or any other orifice.