Pretty easy to rule out the DAC. Turn it off, disconnect the interconnect cables at the pre-amp input end and listen to vinyl only for a few days, or until you hear the popping noise. If you hear the popping noise with the DAC turned off and disconnected front the pre-amp, you've ruled out the DAC as a potential cause.
Question: Do you hear the popping noise through the speaker(s) or do you hear it emanating from the electronic equipment? If speakers, from one or both?