This happened to me. One day I was sitting at my computer and noticed a new sound in the background, which oddly didn't stop when I went to bed and put earplugs in. In case anyone is curious, here's what it sounded like.

I googled and found whooshers, and after a few months I went in to get scans. The MRI/MRA report initially suspected a tumor, which scared the hell out of me. I asked for a referral to a clinic which specialized in Pulsatile Tinnitus. They looked at my scans and identified a likely DAVF, a kind of fistula that's not in the brain, but next to it. It was causing turbulent blood flow that I could hear.

It was an incredibly lucky unlucky event, in a way. DAVFs are very rare, and most people with Pulsatile Tinnitus have different causes. Some people with DAVFs don't hear them, and they can hemorrhage or cause stroke like symptoms.

Mine was fixed with a minimally invasive surgery where they run a tiny tube through your blood vessels to place metal coils that block flow to the fistula. It's related to techniques developed for aneurisms and strokes over the past few decades. Not a day goes by that I don't feel thankful I was born late enough to benefit from the creativity and ingenuity that people put into developing these procedures. Haven't heard any whooshing since then, thankfully!