Troubleshooting:
1) Try a different set of headphones with the TV.
2) Try the same headphones in a different TV.
It sounds like the headphones aren't being pushed in far enough, but perhaps the above steps will help figure out the problem.
If two different headphones have the same issue your TV jack is either defective or there is something inside blocking the headphone jack.
If the same headphones have problems with two different TV's or devices then the jack may be bent.