Hi @njsjl, thank you for reaching us, and welcome to the Sonos Community. I appreciate you describing the issue and for letting us know about it. Let me help you with this.
First I'd like to isolate the issue so we can create a path towards resolution.
1. Is this happening when you play on a specific music service or on all your music services?
2. Do you experience the same while playing the TV?
3. Is there any difference with the speed if your Beam is connected to your WiFi? How about when it's wired to your router?
4. Have you tried removing and re-adding the Sub from the Beam? How about adding the Sub to another Sonos device?
5. If there's no improvement with the speed, you can factory reset your Sub and re-set it up.
After performing the steps above and you're still experiencing the same problem, you may continue working with us over the phone. You can contact our Sonos Customer Care support with your full network setup including the make and model of each device and for more in-depth troubleshooting steps to provide you the best option.
Please feel free to reach out in the future if you have any other questions.
You're always welcome here.