@dipen24739 best case scenario is a driver issue. See if Lenovo has an updated driver for your Ubuntu OS.
If it is not a driver issue then you may be looking at a bad audio amplifier. Connect some headphones and listen if those sound different , i.e. you can hear the sound.
You could also try to start your Lenovo via a bitable USB drive with a different OS and see if that produces the sound. If so, you know that this is a Ubuntu compatibility issue.
Let us know what you find out.