As said by others; see a physician, then a psychiatrist (in that order).
Auditory pseudo-hallucinations may be completely benign, especially if you've partaken in psychedelic substances recent or long since past, but they may also be an early warning sign of (like you said) potential pressure on the brain or abnormality in brain functioning.
And even that might be fine.
Either way, why gamble? Go see a doctor.
By "removed" you mean replaced with a different guitarist (John 5)?
If somebody can't play/tour, they get replaced - the show must go on and whatnot.