My fallout: New Vegas game was working fine untill, recently, I thought that 90% of my sounds went missing. After closer inspection, i found that they were just extremely faint. Not all of them are affected though, oddly. Including Boone's constant Pestering, all music, and the gun firing (but not impact, nor energy bullet sounds). From what google is telling me, this is a extremely rare problem.
Edit.
Ignore
I was too stubborn to test it, but in the end it was my headphones.