Spinning turbine chimney cap - it's grinding and I want to know if I should replace it?

This is a roof vent for exhausting attic heat and humidity take it off your chimney flue it,s dangerous if your were burning wood it will exhaust hot ash and amber's. A proper chimney cap is designed to dampen the ash and amber's but let out the smoke, and keep out the rodent's, someone may have put it there to remove the scent of the fireplace, that's a no no, your home should be pressure balanced so as not to smell fireplace odours. also a home that breathes well smells well. The squealing could also be that the ball bearing in the unit is worn.