New cam...loud clacking lifters. ???

I had the same type of noise once, I decided to put an mp 508 cam in a stock 72 360, I took a peek at the valvesprings, some prying, etc, and the were overtaxed of the point they were almost "sticking"and kind of popping open. Could have been disastrous lol. Put some stiffer springs in, after that it was fine.