I agree that the pop sound is not ideal when throwing a MT kick, as the kick is meant to dig in and follow through the opponent, if the kick is making a pop sound then your probably either 1. not putting your core into the kick and throwing it from your knee, vs. from the waist and core...following through. or 2. your not in the correct range, your hitting the pads at the end of kick where you should be following through, vs. hitting the pads, with a bend in the leg and driving through the target (Thud!).
Now for punches i feel a little different. A pop, sound on the hand pads is a good thing depending on the punch your throwing. If i am working jab, cross, hooks, or uc to the head, i want the pad to pop. The idea is that the pop is indicative of a short quick punch with a quick follow through. If the pad is "thuding" on a head shot your are pushing the punch. In a fight this means over commiting the punch and getting off balance, or pushing the punch into the opponents chin, which does far less damage than a sharp snapping punch that will cause the whiplash effect, i.e: KTFO! A KO punch is not as much about the power as it is putting the punch in the right place and snapping it through the target, causing the "whiplash" that throws off the equilibrium and your opponent goes night-night.
This does not necessarily apply to body shots though, which in some cases you want to make a thud, digging and driving the punch into the oppoent...... like a shovel hook for instance. But for head shots, pop! is good!
(take your middle knuckle and tap yourself in the chin, notice how your field of vision instantly impairs........ do the same, but push the knuckle into your chin, see the difference!):icon_neut