sealed power lifts

ok so heres my problem. i have sealed power lifters in my 500hp engine. i have adjusted these lifts to 1/2, 3/4 and 1 full turn past seated and it still makes a lot of valve noise. i talked to a friend who i highly trust and he has a few ideas. he said to try a little heavier oil like a 15w30. he also said that it maybe that the lifters are not holding enough oil pressure and that would y to try heavier oil. any other input would be appreciated.