My old slosh 20 shv used to do that, but a simple and quick solution sorted it instantly and was casting as quiet as a mouse...:red:
All I do is the usual, remove both sideplates, everything inside gets a good clean and oiled or greased up depending on the components. But before everything goes back together, I oil up the inside of the spool and the outer inside lip of the spool too. This prevents rub between the materials of the frame and the spool, so when it spins it sound lovely n smooth.
If this doesn't work for you I can only suggest you have a badly rusted part within the reel or a component of the reel is damaged.
A hope this helps you sort it out mate.