I bet that this sound comes from the steering column where the steering axle goes through the rubber in the firewall...
The ring underneath the steering wheel for the airbag and claxon contacts can produce noise as well. The rubber part of the steering wheel that is pulled over the back of the wheel (near the airbag ring) can produce irritating noises when it is not properly in place anymore...
The rubber in the firewall will make a whistling sound when it thinks it is in desperate need of Vaseline...
with a minor 600+k