Derailleur twitching in low gears
From what you say the chain tension is now too high. 

There should be a screw that adjusts the tension of the tensioning spring. Sorry I can't tell you where it is: none of the images I can find show it. Check out these sources.

Before adjusting anything take note of the position of each screw, then find the one that you think adjusts the tension and turn it one whole turn and test the result. If it messes up something else, it's the wrong screw so turn it back again. If it changes the twitching and clicking it's the right screw, so adjust it until the it's as good as you can get it. Keep track of how many turns you make, in case you need to start again. If that happens try adjusting in smaller steps. 

Edit: see also the links in this answer.