I had this exact problem in my right earbud. There are 3 mesh grilles on the outside, the top two are used for noise cancellation mics. I assumed the consistent squeaking was because of microphone feedback caused by earwax or sweat buildup, so I cleaned them out with isopropyl alcohol, and the problem got slightly better, but didn't go away entirely.
It wasn't until I used isopropyl alcohol on the speaker mesh, the one inside the tip. I just got some paper towel with 93% IPA, dabbed them a bit, then blew it out with some pressurized air, and now they're back to normal.