When i hold any keys down my sound goes to 0 and wont go back up

i've had this problem for a while and I have done everything that I can find but this still happens. I am on windows 10 and I have had the problem since I was on windows 8. whenever I hold and key down, it doesn't happen every time, but most of the time the sound will slowly drop to zero and if I try to raise it it falls straight back to zero again. Help pls