02-13-2018 08:48 AM
I tried updating the audio driver and reinstalling it.
The sound from the headphones is fine though.
There are no cracking sounds like I've seen in other threads.
02-13-2018 11:09 AM
Try to boot on a different operating system like a live rescue media like here.
Then try to compare the sound from the internal spakers against any external sounds like your headphones.
This would allow you to isolate probable hardware issue with the speakers so you can have your local service center check it for loose contacts or physical reasons causing the muffle internally.
Hope this helps answer your query.
Update us how it goes.