I have had this problem and they are trickey to fix,I usually remove the cable while its in the smallest rear cog,then remove the tensioner/adjuster first,give it a good blast out with gt85 while operating the lever mechanism,then remove cover and cable end, noting spring position.
They are probably the worse shifters out of the sram range,I have recentley changed my x7s to sram grip shift and the difference in shifting is much more posative,and less noisy, as on the front mech you can index the deraliur to find the quietest position over the chainring.
The X9s and Xos are also better, and a worthwhile upgrade. 😉