I have never had a hand held metal detector used to check prior to an MRI. Instead I have been asked questions.
What type of metal is your concern? Pieceings? You can remove them if you're concerned. Teeth fillings or crowns? Not a problem. A pacemaker implant? No MRI, CT scan only.
Not all metal is a problem. MRIs are okay while wearing metal underwire, pants with a zipper, snap or button, and wearing wedding rings is fine too.
MRIs are loud, but they're not 120dB the entire time. Actually, I am not sure that I have ever had an MRI reach that loud — and I have had a lot of MRIs.
MRI is not standard for all cases of tinnitus. It's more commonly recommended for unilateral tinnitus or unilateral hearing loss. I think it's also recommended in cases where a patient has dizziness or if there are any other health concerns, like suspicions of MS.