I had this same issue, similar Roku TV and Yamaha set-up. I was able to resolve by replacing the HDMI cable between the tv and receiver. Make sure you get one that's rated for Ethernet & 20+ gb transfer. If labelled specifically for ARC that will probably be good too!
In case it helps anyone, here's my story. Short version: Changed the audio settings in S/PDIF and ARC from "Auto detect" to "Auto passthrough" and it has stopped the dropouts.
Longer version: Using a 55" 4K HDR TCL Roku TV model 7105X also called 55S403 (manual mentions S401 / S403 / S405). It's feeding a Vizio soundbar with an optical cable. For the last year I've had audio dropouts that last about .5 second and happen every 10 or so seconds. It only happens on OTA channels using an antenna, and it only happens on a couple channels. I've thought it was a signal level issue since I only get 2-3 bars at 40 miles from the towers. Added a high quality booster and it continued but wow, now I get almost twice as many channels thanks to this model. It didn't happen on any other input (Roku streaming, chromecast, firetv etc.)
After trying various options in the settings, I got the dropouts to go away. What I did: go to the menu, choose settings, select audio, select S/PDIF and ARC. Mine was set on Auto detect. After changing it to "Auto passthrough" the dropouts stopped.
Recently after several trouble-free years I started to have many problems with audio skipping and HDCP (digital copyright protection) blocking the video randomly. I replaced the existing cable with a 18GB HDMI cable and everything is OK again.
Was that for the Ultra? The updated version just came out at the beginning of last year. For me, changing the cable... (I'm going direct from Roku to TV, which means fishing the cable behind a wall... Pain in the....) no effect. Now I watch all Amazon and Netflix on my smart Sony TV apps. The other apps work fine except for YouTube.... The absolute worst app.
My Roku is built into the TV (TCL). Don't know if the audio issue described in this thread might be the same as what's happening to your Roku. Guessing there is a lot of overlap in the software between the built in Roku and stand alone. Trying a different cable seems like a decent approach. I had a lot of weird picture distortion from a stand alone Roku a year or two ago and changing out the HDMI cable to a newer one helped clear it up.
This same issue is driving me nuts, and it's a TCL 55 as well. I have now purchased 18gb/s HDMI, no joy. Factory resets, changing menu volume, heck just pulling the HDMI and plugging it back in again. Nothing FIXES the issue. I had it a year ago, did the same tomfoolery, it went away for a while. Now the **bleep** tv is patched again, and it's BACK.
It's only the audio out from the TV or OS, if you use the **bleep** TV speakers it all works fine.
Does anyone at least know if it's a Roku issue, or a TCL issue? A bad implementation, perhaps? Or is it the Roku OS that's at root fault.
For what little it's worth, the new cables are Zeskit 22.8 Gbps ("Amazon's Choice"!) Who tests these things are actually 22.8 Gbps? Anyway, they work. They're so sturdy that bending or twisting is a bit difficult.
@Shryke do you use an optical S/PDIF cable (red light comes out one end) to feed a sound bar or what is your external sound system connection? You could try to switch to using an analog cable from the TV to a sound bar if you're using one. The audio should still sound good, and there's a chance that it'll stop whatever digital glitch is going on. This cable is under $5 and is worth a try...it'll bring a stereo signal to the sound bar (not Dolby 5.1 or 7.1 surround, it can still sound quite good.)
Does it happen with any programming on the tv? Over the air TV, streaming, DVD player, etc.? Mine was only on over the air channels from an antenna. Changing something in the Roku settings (again, inside the TCL 55" TV) seemed to solve it.