2000 Kia Sportage injectors

I just bought a 2000 sportage and when you first start it up after it has been sitting you can hear the lifters knock, but than it quiets down. I took it to the mechanic where I bought the car and he said it is the the fuel injectors. He said they do that on those Kia until they warm up. Is this correct or is he pulling my leg.
Thank you,
Mary