prasanna,
It sounds like your wall chargers might have damaged your player
. However, rather than jump to conclusions, try:
1. Try another set of earphones instead? Maybe coincidence, earphones crapped out?
2. Try the radio function and see if you can hear the radio ok?
3. Try also the recording feature too to see if you can record your voice and hear it back.
4. Try formatting your player as well if all the above doesn't work. Then copy the files across to see if that helps.
Does your player still function normally other than the sound being screwed?