Roku Class 4K HDR LED Select Series Smart TV Sound changing on its own
I recently purchased a ROKU 55R4A5R 4k LED TV. I am having issues with the sound. It is connected to a VIZIO SB3830-DO via the HDMI ARC connection. During some programs when a commercial comes on the sound drops to barely audible, then returns to normal level for some commercials, or when the show comes back on. During other programs, the sound will drop for 2-4 seconds then return to normal. Now here is the kicker, this TV replaced a Hisense ROKU equipped TV via the same configuration (HDMI ARC) and never had this issue during a two year life span. It started the first day we turned the new TV on, so it appears that the TV is the culprit.
I have done a lot of trouble shooting like, checking the settings for both devices, turning everything off for a while, changing to a new HDMI cable that said it was for ARC, and looking for info online. I'm stuck as to why this issue is randomly happening, so decided to turn to here.
Wondering if anyone else had this problem and how they resolved it. I could return the set to Best Buy, but know the first thing they are going to do is say it's the soundbar. Any ideas are welcome.