The engine is a mid 70's 350 Olds bone stock with unknown mileage (I've put 30k on it since pulling it from the junkyard). It has the stock flat tappet cam and has never been apart. I've run a number of different oils brands and weights, synthetic and non synthetic. I drained the Rotella Syn 0W40 out with 3k miles on it (had not used any noticeable amount in 3k miles) and refilled with 20W50 VR1 Valvoline which I've used last year. My engine has always been slightly low on oil pressure only at a hot idle, and this oil raised the pressure up noticeably but now it has a tick under the drivers side valve cover that I can hear just barely from in the car with the window down. Not sure how a heavier oil can cause that on a hot engine but its there. I think this is the only non synthetic oil I've run in this car other than for winter storage one year. Maybe the synthetic kept it quiet? Any thoughts? I like the higher oil pressure but don't like the noise.