Recently this 2005 Volvo XC90 2.5T AWD, AW55-50 started to make this burring whine noise as the vehicle shifts into 2nd gear. As the car revs up and ultimately shifts into 2nd the noise occurs with 100% reproduction just as the tachometer crosses over 2k RPMs. This noise began occurring at 170,762 miles on the engine. The noise is coming from somewhere in the drivetrain I'm guessing? Maybe the transmission or the gearbox or something? I'm not too sure where its coming from and hope someone can identify the noise for us.
Is this sound an instance of gear whine? I annotate multiple instances in this video I just uploaded to YouTube using green text overlaid on the video: Volvo XC90 Mystery Sound (gear whine?)
I haven't fully identified the source of the sound but I set a few microphones around where I suspect the sound is coming from. This first recording is focused on the transfer case aka bevel gear. One of the microphones (the contact mic) is clipped on to a rib beneath the transfer case like you see in the photo below, the other (a lavalier mic) is taped to a cross frame member facing up to the same transfer case (which as you can see is leaking some old greasy dehydrated oil and gunk).
I'll be checking the bevel gear oil level soon and maybe drain and fill it and also take a few more recordings to zero in on the sound by studying which mic pics up the loudest. As always any help folks can offer will be greatly appreciated!
