Headphones have static noise with Ubuntu 21.04 on DELL Vostro 2520
 

There is a static sound coming to my earphone when i use the laptop connected with some external source like extension cord. this problem was in Ubuntu 20.04 and then i had upgraded now also it is in Ubuntu 21.04. That sound is making my ear goes numb and also paining . I had tried many solutions from the forum and many other Ubuntu websites but non of them worked. That noise cancellation is the shit thing that doesn't work , also a loop-back option is not available in the alsamixer.

One thing is that my battery is obsoleted that's why is use the laptop as connected to the power source always.
EDIT- This laptop is at least 8 year old working on Ubuntu 21.04 64bit ,obsoleted battery, Intel® Core™ i3-3110M CPU @ 2.40GHz × 4 ,Intel® HD Graphics 4000 (IVB GT2),
Sound card- Intel Corporation 7 Series/C216 Chipset Family High Definition Audio Controller
KINDLY HELP

Very likely this is a hardware issue, specifically a grounding issue inside of the machine or between the machine and your site's electrical wiring (if software changes are having zero impact). The short answer is: you cannot realistically 'fix' this on the machine, but you can probably bypass it by using a different soundcard - cheap USB devices are a very popular solution here.