Light knock when starting car

What is your question?

I hear a light knock when engine starts up then goes away but when I add pressure to throttle I can hear it ever so slightly . I just replaced mase air sensor could it be because of that. I had it diagnosed at auto zone and had no code and car has only 71k miles on engine so I don't want to harm it but also it could be nothing Also I looked for anything lose and didn't see nothing exhausts is quiet as a mouse so I don't know why it's making noise although oil life is at 68 percent so would a oil change be the issue though all reads say everything is normal