A 3% margin of error means that if the same procedure is used a large number of times, 95% of the time the true population average will be within the 95% confidence interval of the sample estimate plus or minus 3%.
The latter is a fairly common problem which is associated with people who have the condition known as hypothyroidism. Despite what many people think, tinnitus is actually just a symptom of a larger underlying problem. Hypothyroidism is just one of the many health problems which can cause tinnitus to become a problem. In most cases when the thyroid dysfunction is treated, the tinnitus will resolve itself. There have been some cases of people with this condition who suffer from long-term tinnitus, though that is usually not the case.
People who produce too much thyroid hormone (hyperthyroidism) are often treated with radioactive iodine or anti-thyroid medications to reduce and normalize their thyroid function. However, in some cases, treatment of hyperthyroidism can result in permanent hypothyroidism.