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Hi Sue, The ringing in the ears is called Tinnitus. It can be a side effect of medications (check what you are taking) or for me, it can also be a sign that a migraine is on the way. It could also mean a number of many other things, depending on other symptoms you may have.
Consult a doctor if tinnitus comes on suddenly and is accompanied by hearing loss or dizziness. A sudden ear ringing may be the result of a newly prescribed medication, in which case the prescribing physician should be alerted to the problem. With the frequent difficulty of determining a diagnosis or underlying cause, solutions to tinnitus can be elusive.