Squealing/Sqeaking in left bud

My left earbud has a repetitive squealing/squeaking sound when used in either noise cancelling mode. If i turn off NC, the sounds goes away. The volume in the left side also seems quieter. I have had this issue once before more than a year ago when they were under warranty where I sent them in for successful repair (or whatever they did). I suspect that earwax builds up inside the buds under the protective screen over time but can't verify without removing the screen. I'm willing to do some disassembly if it might fix them. Any suggestions?