Audible 4020 Hz Morse code emitting from BPI-R4 PoE

Banana Pi Router design BPI-R4(MT7988)
1

Hi everyone,

I was wondering if I could get some suggestions on actions I could take to reduce the ~4020 Hz pulsed (like random Morse code) tone that my router is emitting at all times. Please share your suspicions for the underlying cause of such a sound, such as PWM fan speed control, or any other activity the BPI-R4 performs in bursts of ~4020 Hz.

Details: BPI-R4 PoE with included fan and aluminum heatsink

Not using SFP port

Using USB Type C power

Using microSD card

BE14 Wi-Fi 7 NIC with only 5 GHz enabled, passively cooled

OS: OpenWrt 24.10.0, r28427-6df0e3d02a

Kernel: 6.6.73

2

Coil whine, perhaps? Maybe try switching the adapter from Type C to a power adapter and see if it improves?

3

That fixed it. I swore I read someone on here saying USB PD would somehow provide cleaner power, but now as I search for it again, everyone is saying to use the included DC power adapter. I don’t know what led me away from using that. Thank you!

To be clear for posterity, the coil whine sound came from the BPI-R4 board itself in a pulsed manner, and also from my USB power brick (Minix Neo P140) in a continuous tone.