Sennheiser CX300s louder in 1 ear than the other, Fixable ?

[Grosser611]

As the title would suggest, I have a pair of Sennheiser CX300s. The other day when I went to use them the left one is about 1 third quieter than the right, not enough to be totally unlistenable but enough to be very annoying. Is there a simple way to fix these or what could the problem be even ? They only cost me $30 so O'll probly have to just keep them as my cycling headphones as they keep the sound out well and I only keep one in at a time.

[audio amateur]

Make sure the jack connection is secure, and perhaps try them on a different music source.

[Grosser611]

Make sure the jack connection is secure, and perhaps try them on a different music source.
I've done both, neither worked unfortunately :( Also its not only a loss of sound in db but a loss in sound quality too. It sounds very dull and much more like a $20 pair of headphones not $100. Any ideas ?