Turns out.... this guy had the same noise and fixed it by replacing the oil trap.

https://www.swedespeed.com/threads/2016-xc90-oil-catch-pcv-easy-fix.640578/

 

Yep, if the whistling stops when you remove the oil filler cap, it’s likely an oil trap. Cheap and easy part to replace.

 

I just bought a Volvo OEM off of ebay (brandy new) for $90. I didn't want to play around with aftermarket stuff, and liked the idea of saving $100 over our favorite online stores... fingers crosses..
Would a bad oil trap be a cause for higher than usual oil consumption?

 

What year is your XC90? If it’s a 2016, it will be the crappy piston ring design, requiring new pistons and/or a whole new engine.

 

Most likely the oil trap. Easy to replace on that engine for sure.

The older models did have oil consumption problems due to the piston and ring design, as mentioned above, but that won't cause the high suction you have going on. I'd say start with the new oil trap, and then see how it affects the oil consumption. If you're still using a lot of oil, then you probably have a piston/ring issue.

If you're in the USA, I believe there's some kind of class action lawsuit and campaign to replace the pistons and rings with updated parts.

 

It’s an early 2016. .

 

I replaced the oil trap. Whining noise is gone. Yay. Noticed that the hose connected to the oil trap had a small crack in a spot where it shouldn’t effect the seal to the oil trap, but I will replace this hose too.
I still have the P0171 code (reset it using Obd scanner tool).
think it could be the hose? Should I move on to replacing MAF? Or O2 sensors (not super cheap).

 

That's good, the hose isn't likely to affect anything, but always good to have the hoses in good condition as well.

That fault code will likely come back right away because you are unable to reset the fuel trim adaptations with a simple OBD scanner tool. Usually you need the factory scan tool or something that can do more than just read codes. You could try clearing the fault codes and then leaving your battery disconnected for a while, although I'm not sure if that will do it or not either. The root of the problem is most likely fixed now though, with the replacement of the oil trap.

 

I took the car for a nice 1hour drive, used the scanner to reset the DTC and it hasn’t come back yet. So I think it may be resolved now.
Thanks for the feedback on a regular scanner tool (I use a veepeak with the “Car Scanner” app for iPhone).