Hi. friend has weird habits like snapping fingers for no reason, wearing a neck brace but no injury also said he heard voices in mind before. ideas?

Not definite, but...: Snapping fingers can be a nervous habit, and normal. Wearing an unneeded neck brace seems odd, possibly delusional. Truly hearing voices is an auditory hallucination. In fact this CAN be a normal part of grief or separation, such as "hearing" your dead grandmother. Unfamiliar voices making assertions is common in psychotic disorders- depression and schizophrenia. It's possible he needs help.