Could it be that the popping noise is the transmission? There is a simmilar problem like yours, where owners hear the popping noise coming from the rear. This only happens when the car comes to a complete stop though. The solution to that problem is the transmission needs to be reset. I'm not sure if this is the same problem as yours.
It could also be that when you let go of the brake, you get that "popping" noise as well.
I highly suggest you take it in.
Hope I helped.
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