Hey guys I've got some kind of vacuum leak or just bad sensors here and could use some help/opinions. My xc90 3.2l has less that 93k miles on it and it's at first started throwing a code P0430. The engine light would randomly come on and off. Then it started throwing a code P0420. So immediately I thought ok so one 02 sensor went and then another. I put it on the back burner but did an oil change. My dumbass left the oil cap off for atleast 2days during the week until I pulled in the garage and saw it. I put it back on, checked my oil which was good then decided to scan my car again. I got the 171 and 174 codes on top of the older o2 codes. I reset the codes and hoped the new ones wouldn't come back. But they dide. So I decided to just look around the engine bay a bit and found nothing...except that when I pull my oil dipstick I get a honking/goose sound? Like a constant GOOSE (the waterfowl) sound. Never heard that in my life...I'm thinking PCV system? Is this bad and mean I need to replace it? Also, any ideas about my 420 and 430 codes? I don't seem to have an exhaust leak and the fact that it goes away and comes back makes me think it's a sensor but before I end up replacing all 4 I'd like to exhaust all other options...no reason to throw parts at it right? Thanks guys!