How to fix realtek hd audio losing first second of playback of notifications, crack and pops (cause: device being switched to low power mode all the time by driver):
use regedit to edit
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4d36e96c-e325-11ce-bfc1-08002be10318}\xxxx\PowerSettings
where xxxx - number from 0000 and up, look for DriverDesc value of "Realtek High Definition Audio"
Change ConservationIdleTime to ff ff ff 00
Change PerformanceIdleTime to ff ff ff 00
where ff ff ff 00 - time in seconds. Driver default values 03 00 00 00 - 3 seconds, which is causing all the problems. Value of 00 00 00 00 (no sleep timer) is not supported by realtek driver!
reboot to apply.

more details about audio device class inactivity timer: https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/audio-device-class-inactivity-timer-implementation

If you are missing separate playback and recording devies in realtek hd audio (like I do, using headset for skype and listening to music from speakers are convinient):
Search and download AudioDevice_sky.rar - realtek driver configuration editing tool.
There is no RTKHDAUDIO.DAT file present, it's ok. Go to driver policy tab, press "get policy driver" button, press "save".

Open "JackCfg" subsection, and enable "10-PBIndependentSupport", "14-RecIndependentSupport".
Press "save" again, reboot to reload driver.
You can now see separate headphones and speakers (playback) and microphone array and headset microphone in recording in windows "sound" control panel.

Right click on wifi icon (right bottom of task bar) and choose Open Network & Internet Settings.
Now you are at Network Connections window, Status tab (win10), click on Change Adapter Options
Right click on your enabled network adapter (Wi-Fi) and click on Properties
Now you are at Wi-Fi Properties window, click on Configure button.
Click on Advanced tab,
You will see properties in a multilist window, choose Transmit Power.
There will be a setting of selected property in the right side, choose the 4- Mid-High or 3- Mid option (I use 4, and default was 5-Highest)

To fix this, you need to switch "High Definition Audio Controller (Microsoft)" to MSI mode. In the registry in the key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\PCI""YOUR HD AUDIO PARENT""\DeviceParameters\Interrupt Management\MessageSignaled\InterruptProperties\ "MSISupported" Change to "0x00000001"
YOUR HD AUDIO PARENT see in Device Manager\Sound, Video and game controllers\hdaudio, realtek and other\Properties\Details\Parent

I ordered a Y540 for my cousin and he was really disappointed, because of the audio issue.
I did some investigation and those sneaky lenovo engineers already created a fix, but hid it very good.
The problem mainly seems to be, that the CPU voltages ramp up and down very fast for power saving, leading to a crackling noise at every transition. That also explains, why the sound is fine when gaming, as the CPU is always running at full load.
The fix Lenovo implemented was simply to make those voltage transitions slower and therfore reduce/remove the crackling sound.

Here are the steps I did to fix issue on my cusins Y540:
1. Download an install the latest BIOS from Lenovo's site (BHCN32WW)
-> This will take through a reboot and all, just let it sit and don't touch your notebook while updating
2. Shut down your PC
3. Use a small pin (for example a SIM-Card removal tool from your phone) and poke it into the whole between the USB Port and the Power LED in the right of the Notebook
4. The notebook should start and give you a small menu
5. Select "Setup Bios"
6. Select "Configuration" by pressing the right arrow key
7. Select "Slow slew rate for ia domain" (arrow down) and press enter
8. Select "fast/8" and press enter
9. Press the F10 key to reboot

When you boot into windows now, the sound should be good.
I can't really tell what other implication those settings have (maybe the systems gets unstable, or a little less power efficient), but it worked for us.

PS: You don't need to use a pin to go into the BIOS, just hold shift when pressing restart; go to Troubleshooting; select UEFI startup.