Hi Hoà Lê,
Thanks for all the testing you’ve already done. There are a couple of things I’d check next that should help narrow down whether this is happening at the Windows audio level or specifically when the Bluetooth microphone mode kicks in.
First, please try the headset with Sound Recorder:
- Open Start, search for Sound Recorder and open it.
- With the Bluetooth headphones connected, start a short recording.
- Speak into the headset microphone for a few seconds, then stop the recording and play it back.
Does the buzzing start there as well and does the recording pick up your voice?
I’d also like to know which Windows build and Bluetooth adapter you have:
- Press Windows + R, type winver and press Enter. Please share the version and OS build shown.
- Right-click Start > Device Manager, expand Bluetooth and share the name of the Bluetooth adapter listed there.
- If you remember, did this start after any Windows or driver update?
One more setting is worth checking:
- Open Settings > System > Sound.
- Under Output, select your Bluetooth headphones.
- Expand Output settings > Format.
- If Format when microphone is active is available and currently says Stereo, change it to Mono temporarily and test again.
If you don’t see that option, that’s fine. Not every PC/headset combination exposes it.
You can also select the headset microphone under Settings > System > Sound > Input and temporarily set Audio enhancements to Off, if that option appears.
Please let me know what happens with the Sound Recorder test and what you find under the microphone-active format setting. That should help narrow this down further without repeating the troubleshooting you’ve already done.