My 8yo complained about it, so we went to the doctor and, for him, it was a result of sinus drainage in his ears. They did a quick hearing test and it was normal.

Definitely get it checked out. Can be as simple to deal with as earwax or an ear infection or as difficult/permanent as noise-induced hearing loss coupled with tinnitus.

Earbuds/headphones aren't the only culprit behind ringing in the ears, btw. Does your child go to concerts? Play in band/orchestra? Help with lawn care (lawn mowers, leafblowers)? There are so many causes of noise-induced hearing loss and tinnitus.

http://www.nidcd.nih.gov/health/hearing/pages/tinnitus.aspx

Could be as simple as earwax up against the ear drum. Drugs like Advil can cause it too. But if it's really bugging her, she should see a doctor

Get it checked out. Is it both ears or just one. Any new meds? There are many possible causes.

Ringing in the ears?
My 9th grader is complaining a lot. no ear buds for her so Im not sure why.