Thank you for advice! For few months everything was ok, and this problem occured suddenly. And considering that volume level changes sugnifically while in use, can it still be filter cludge?

Hello! I have a problem with my pfe 022: volume level dropped by ~40-50% and now it changes smoothly up and down(but not above mentioned 50-60%) while I listen to it. And left piece is even much quiter. I can see no cracks on it and cable is ok. What can I do about it?