Muffled, low quality sound

As soon as I load into the main menu the sound quality degrades significantly and does not improve neither in other screens nor during gameplay. Restarting does not resolve. Using bluetooth headphones.

EDIT:

I have figured out what is happening. The degraded sound quality is due to Windows 11's "Handsfree Telephony" feature. When the mic turns on (which it does precisely when loading into the main menu), Windows 11 switches the bluetooth headphones from high-quality music mode (A2DP) to hands-free call mode (HFP/HSP), which uses a very low-bitrate codec so voice can go both ways.

Problem is, I have actually disabled the mic on my bluetooth headphones in Windows Input Devices settings. Instead, I'm using a dedicated mic. But something about Marathon specifically triggers the Handsfree Telephony to activate anyway, despite the headphones only being used for output and a separate mic being used for input. This doesn't happen to me in other apps such as Microsoft Teams or Discord or even other online games such as Overwatch, so this seems to be a bug in how Marathon is trying to access the output audio device. I hope this helps. For now the only fix seems to be to either use wired headphones or disable Voice Chat entirely. Disabling "Handsfree Telephony" service in the bluetooth device's settings triggers Marathon's sound to perpetually cut off then cut through again multiple times per second. Please feel free to contact me for more information if you need it. Thank you.