Loud and jumpy rear derailleur

[catbehemoth]

Hi Alex, thank you for creating this site, so many useful tips and hints!
I have a problem with my rear derailleur, everytime I jump off from a curb or riding a bumpy road, rear derailleur is making lots of noise by the sound of it jumping up and down hitting lower part of cassette. I may be wrong with terms though, as my "cycling" english is quite bad.It happens disregarding what gear I use.
I judge comparing to my mate's bicycle which doesn't make much noise at all at the same conditions. Perhaps there is a screw I've missed I can adjust the tension with?
Thanks you
Alex

[Skyguy9999]

You're having the top derailleur pulley bump into the rear cassette?
See <a HREF="http://bikeride.com/adjust-rear-derailleur/">this video</a> about 1:28 in, which might help. It might be worth checking the tension of the derailleur cable, as well.