I had the same problem. Some folks say to dab a bit of some kind of stickum gently onto the speaker screen to get the dust and debris to cling to it, like a bit of the sticky edge of a PostIt note. Tried that—no luck. Tried vacuuming—no luck. Then with COVID, I was using alcohol wipes all the time at work in a pretty much deserted building, and I read that I should also wipe down my “third hand”—my phone. I did, without thinking about the speaker, and the sound is like new. This was not a liquid, but a moderately damp alcohol wipe. I think the fumes did something. I doubt that liquid alcohol entered the opening. Hope it works for you.