Surface Pro 4, annoying noise from the back!

Presumably it's PWM (Pulse Width Modulation). The screen backlight is rapidly switched on and off rather than true dimming. The electronics tend to make a screaming noise as a result unfortunately. I've noticed the keyboard backlighting is even louder. 😩

I've had my Surface Pro 4 for a couple of weeks and recently started noticing a screeching sound from the back of the device, more obvious from the top of the vents. It's a bit like a very high pitch modem noise. It's not hugely loud but quite noticeable in a quiet environment.

It's not due to wireless or Bluetooth as it continues when in flight mode. Neither is it affected by muting/unmuting the speakers. It's not affected by screen brightness either. It doesn't do it all the time but seems to now be more often than not and I can't be sure whether it's always been like it. When I drag the pen on the screen the noise is partially changed to a white noise sound but the modem-like noise is still there.

Has anyone else noticed this, or could my device be faulty? It's starting to be quite irritating. My wife's Surface 3 also makes a white noise sound when a pen is in dragged on the the screen but doesn't make a screeching noise.

Well, I've done some digging and it seems this noise was reported way back on the first Surface Pro. It appears to be to do with when the CPU enters various c-states (when idle).

There is a thread here about it.

One of posts suggests the following workaround, essentially disabling the idle state:

You can disable the ACPI C2-state and C3-state by setting a registry key. To do this, follow these steps:

1. At a command prompt, run the following command:

reg add HKLM\System\CurrentControlSet\Control\Processor /v Capabilities /t REG_DWORD /d 0x0007e066

2. Restart the computer.

Note The computer idle power consumption will increase significantly if the deeper ACPI C-states (processor idle sleep states) are disabled.

To continue to benefit from these energy-saving states, remove the registry key that you set in step 1 after you install the hotfix that this article describes. To do remove the registry key, follow these steps:

1. At a command prompt, run the following command:

reg delete HKLM\System\CurrentControlSet\Control\Processor /v Capabilities /f

2. Restart the computer.

I have found this improves the noise a lot but the question of course is what adverse impact this will have on battery use or heat etc. Time will tell I suppose.

It's pretty annoying that this has been known about for this long and Microsoft/Intel have not addressed the problem properly.

So I'd like to know for sure one way or the other whether other Surface Pro 4 users can hear this noise from the back of their device (easiest to hear from the vents at the top near camera).

My SP4 M3 model has the same. Funny... if you start a watch panel (where you adjust time).. the noise will be modulated every second, every time second arrow is moved in the analogical watch on the screen. Definitely it has something to do with changes in the screen.. pen, content changes..

Hello GiovanniSm

When did this start happening?

Can you confirm that Surface is fully up to date?  Did all updates install successfully?

Do you notice this happening under other circumstances, beyond dimmed screen?

Best regards