Hollow sound when chewing / pulsing sound when lying down

About 3 weeks ago, I noticed that suddenly there was a strange "hollow" or "metallic" sound inside my head whenever I was chewing or clicking my teeth together. I also noticed that there seemed to be something in my right ear, and when I moved my head side to side I could sense it a bit. Both sensations are now gone, but a new and I'm sure related issue has arisen in the past few days.

Now at night when I'm lying down I can sometimes hear this pulsing sound in my right ear. It's hard to describe but maybe something like a mix of a whoosh and a drill. I googled it and it seems to be something called pulsatile tinnitus, because the sound is in perfect sync with my pulse.

Does anyone possibly have an idea of what could be the cause?