The low pitch noise you hear is probably the open string note.

When lifting your finger off the fretboard you have to be careful not to pull the string in any way. What you are probably doing now is almost a pull-off to the open string.

Try to lifting your finger straight up and minimize any lateral movement. You can also add a small amount of palm muting. Not too much, just enough so the string won't ring but this is harder to do on smaller strings.