2002 Chevy Camaro Noisy lifter

I have just recently changed the oil in my camaro. Over the last 3 weeks, I have noticed on several occassions that when I cranked the motor, I am getting a very loud lifter tapping noise on driver's side. It usually goes away after about 3-4 minutes. This problem started after having my oil changed and had synthetic blend motor oil put in for the first time. Some days there is no noise and on others there is noise after sitting over night or after just a few hours. This is the first time synthetic blend oil has been used in my car. I change oil every 3000-4000 miles religiously and have no other mechanical issues with the car. Also after this last oil change, I noticed that the oil pressure has been running below what it had been running. Used to run around 50-60lbs at crank-up and above 40lbs after warming up. Now it runs 40-45lbs at crank up and above 35lbs to just under 40lbs after warm up and at highway speeds. My question is: What could be causing the lifter noise and lower oil pressures? Do I need to go back to a conventional motor oil? Am I looking at a potential major problem with this motor?