You can't. They will always pop. As far as I know. Mine do the same thing. I pull my knees toward each other and/or twist a little and they both pop in turn, and my lower back always pops, if I hang my weight on it or do dips, etc. Then again, I'm just a poppy person, I've even popped joints that aren't really joints, like the fusion between metacarpals by wiggling my hand bones. I've popped every joint in my body at least once, except for my pinky toes, they appear to be fused in their deformity.
But if they are popping every rep, your joint or joints may be hypermobile and you will want to work to fix that to avoid wear and tear outside the normal ROM. This is the reason I gave up sit-ups permanently in my teens. The reps always popped, it added up to burning pain and damage, so I just refused to do them. Gym teacher actually understood.
So, are these the "pop once and done" type, or more the "constant pop every rep" type?