Magnifi Max SR Intermittent Surround and Sub issues

I've had my Magnifi Max SR system for just over a year, and I have recurrent issue that is driving me nuts. Let me preface this by stating that the system was a gift, and it was apparently purchased refurbished, so Polk Audio has been unwilling to provide any warranty service.

Periodically, one or both of the surrounds will crackle when media - any media - is playing. Generally, resyncing the system will take care of the problem, at least temporarily. After the last sync, everything was normal for a couple of weeks, now the sub is popping when media is NOT playing. In fact, we were awakened by the sub popping quite loudly in the night. Nothing was on, no one was using it.

I have gone rounds with customer service over this. I've made sure it's connected to our 5ghz network, checked the firmware in the Google Home app, moved other wireless devices away from the soundbar, and I've synced the system repeatedly, but it just keeps coming back. Do I just have a defective unit? I love the system when it works, but it makes me want to do awful things when it doesn't.