Fiat bravo.S Ticking Noise from Engine please help!?

The Ticking noise occurs intermittentle,when engine warm's up it Disappears then can come back at any time.could it be oil Filter.I have not Fitted Fiat Filter but a cheaper version!oil changed Regularly 10-40 oil Jet's cleaned under Rocker box? tappits o.k (Engine was overhauld Because of this !