Objective tinnitus is a rare form in which other people can hear the noise in addition to the sufferer. The noise, detectable to someone else with a stethoscope, may be caused by blood rushing through the carotid artery, TMJ, the eustachian tubes opening, repetitive muscle contractions, or blood flowing in the jugular vein. Could be benign or the sign or increased pressure inside the head from something nasty growing in there.

Subjective tinnitus is less well understood. Anything from the ear canal to the brain may be involved. Sounds can range from a metallic ringing, buzzing, blowing, clanging, or popping, or nonrhythmic beating. In one survey of 1687 tinntius patients, noise exposure was responsible for only 24% of the cases. No known cause was identified for 43%.

Things besides noise reported to exacerbate or give you tinnitus: food allergies, salicylates, naprosyn, ibuprofen, aspartame, marijuana, alcohol, caffeine, tobacco, high fat intake, high sodium intake, non-steroidal anti-inflammatories, aminoglycoside antibiotics, anti-depressants, loop-inhibiting diuretics, quinine in anti-malarials or tonic water, oral contraceptives, chemotherapy, lyme disease, ear wax buildup, high blood cholesterol, mercury amalgam tooth fillings, acoustic neuromas (ear tumors), otosclerosis, and being hit in the head with a cast iron skillet.
Okay, any head trauma. Doesn't have to be a skillet.