aaahza,
It could be a few reasons why.
1. You could have wound it on the wrong way and it does not come out.
2. The eyelets have worn and the nylon is touching the plastic.
3. The nylon is old and gone hard and nylon is sticking together inside the head.
How to fix some of the issues:
1. Wind on in correct direction.
2. Replace worn eyelets or replace the head.
3. Place nylon in hot water to soften up and also when putting back together use some baby powder to lubricate the nylon.
Let us know what you find wrong.