S60 AWD L5-2.5L Turbo VIN 59 B5254T2 (2005)
Correct position of front area shown with dotted line here.
NOTE: This shape is normal in the rear area.
Hint: Use a mirror for this check.
Also inspect the alignment of the climate box housing and the collar so that there is no gap as indicated here.
If necessary; reposition for better sealing.
Inspect / Modify the Recirculation Seal
A similar sound may be heard with recirculation ON (door closed) if there is a small gap between the rubber door seal and plastic housing.
This may happen if the recirculation door has a rounded shape or if the pressure of the door is insufficient.
If needed; clean the rubber surface with P/N 1161436 or similar and apply felt tape (P/N 9511099) onto the rubber seal of the door as shown.
Reassemble
Reinstall parts in reverse order