Hello, MohanVadivel.
I understand that you are having sound issues with your MacBook Pro. You have already performed some impressive troubleshooting steps, and I’m glad to lend some additional assistance.
I would like to see if the sound is still distorted in both safe mode and in a test user.
If the sound is typical in safe mode, we’ll know that a third-party driver or application causes the distortion.
If you don't hear the sound distortion in the test user, we’ll know that it isn’t a system-wide issue and can focus on what might be causing it on your admin account.
Use safe mode to isolate issues with your Mac
How to test an issue in another user account on your Mac
If you hear the distortion in safe mode and in a test user, I would contact Apple Support to look into your service options.
I hope this helps. Please keep the community updated!
Be Well.