I recently had my Dell G3 3579 fixed, it had an issue with the GPU. The mainboard was replaced.
When I got it back, all audio that came out from my earphones was also going into the mic channel, so when I played games while in a call the other people could hear my game sound.
I fixed it by installing a different audio driver from Realtek. Now, instead of having "Speakers/Headphones" in the sound control panel tab it has two separate devices, "Speakers" and "Headphones". This worked, but when I don't have headphones plugged in it makes an occasional cracking sound from either the left or right in-built speaker, with no apparent cause. It happens randomly, but it's quite often when I launch a program or a program plays a sound.
I went to Dell's site and downloaded the latest audio driver for my laptop and now the "Speakers/Headphones" are combined again. The popping noise seems to have stopped, but my audio output is going back into the microphone channel again.
I've tried disabling/enabling audio enhancements, changing the audio quality setting, and pretty much everything in the properties tab of the Speakers. Does anybody know what's causing this?
I also have this issue without any previous issues mentioned by the OP.
It happens occasionally, without any other playback and happens always several times in a row with random few-second intervals. Then it stops for some time. The sound comes from speakers, without anything connected via jack.
The sound resembles that of a sudden disconnection of headphones, when the jack pins get short-circuit for split a second. It sounds just like power surge.