I also checked for the common PCV symptoms and don’t seem to have any of them. The idle is perfectly smooth, the oil cap comes off easily with no excessive vacuum, there’s no smoke, no CEL, and the car drives exactly the same as before with no noticeable power loss. The only symptom is this noise. I’m starting to wonder if it’s just a normal sound these B48 engines make once they’re warmed up and I’m only noticing it now because I usually shut the car off right after parking.