My Mustang sits for a week at a time. I drive it on weekends. Upon starting, for a few seconds there is lifter tapping noise. Then it goes away and the car runs fine. Actually better than fine. I am using Mobil 1 5w-40. It has 1300 of zinc and 1100 of phosphorous. I picked it for that, and I thought a synthetic would protect better since the car is not used every day and may sit for a week or two, and several months in the winter. Should I try another oil to stop the lifter tick at start? Thanks.