Recently had 1964 GTO 389 professionaly rebuilt. Have appx. 1500 miles on it and have changed oil 3 times using Lucas zinc additive. After sitting and cold in the morning, it rattles like rod noise until pressure is up (2-3 seconds). It is getting progressively worse and I was told there is an oil check valve/spring where the oil filter mount bolts to the block that may be bad. I wonder if it is just a loose motor? Carries 50-60 psi once running. Any ideas?