rockers ticking

[pqc3]

i have a brand new motor in my car with 500 miles.when it start up cold it runs fine but after about 20 minutes it developes a slight steady miss and the rockers begin to tick.oil pressure is 70 to 75 cold and 40 to 50 hot at idle.
any ideas?
thanks.
also,when you raise the rpm or drive down the road it the miss goes away but it still ticks.it has a cam and springs but im not sure what the specs are.