2004 XC90 Whirring sound passenger side front fender?
 

Hello, I'm new to this forum. My 2004 XC 90 5 cyl turbo has a strange whirring sound coming from the area behind the passenger side headlight and washer reservoir. It can be heard from 10 feet away and also inside through the passenger side dash heat vent. It's there engine on or off and seems to never stop. Sounds like a dry leaf in a heater fan. Always at the same speed. Anyone have any theories? Thank you in advance.

does the noise change with blower speed? can you hear the noise when you open the hood and listen in? Check to make sure your cabin air filter is intact or debris may have gotten in.

New Clues to Whirring Passenger Front
 

Thank you for the reply, but here are some new observations: (1) With the warmer weather I tried to open the sunroof and found that it did not work. It always had before. I pulled fuse #14 to see if it was blown (it was not) and as soon as I pulled it, the whirring sound stopped. Put it back, and it began again. (2) Before I did the above, and after the car had been off for several hours, I noticed that the noise had stopped. As soon as I unlocked it with the keyless fob, the whirring started up again. One note: I did the lock/unlock routine manually with the key three (3) times with no change to any of the above.

The siren for your alarm is located inside the front right wheel well underneath the plastic wheel well lining. When it goes bad, it messes up the sunroof controls somehow as they "report" via the same circuitry. Putting the noise together with the sunroof issue, it seems plausible that it might be your siren.

Thank you. That sounds very plausible as coincidentally I have a "service alarm" notice came up as well. I will delve into that this weekend and get back to the group.