tonal hum at low speeds first thing in the morning

[heleads]

I have a 2019 Volvo S60 with under 40K miles. Just recently had the breaks and routers replaced by a Volvo dealership. Within a week after (and this may just be totally coincidental) we started noticing a low resonating hum (almost like a haunting sound, definitely not a squeaky belt or scratchy sound). The sound is only heard in the mornings or after the car has sat a long time and when pulling out of our driveway (gravel) or parking lot. Sound goes away after speed increases above say 15mph. Sound is not related to applying the breaks nor the gas. I have heard it going backwards, going straight, but mostly the sound is initiated when the steering wheel is being turned. The sound comes from the front maybe slightly from the passenger side. A local mechanic says it could be the struts as he saw some wear on them but the car has less than 40K miles on it! He lubricated the struts but the sound returns a day or two later. Other similar posts suggest the could be a defect in the bushings on the struts and that there was a bushing replacement kit?? Dealership wants hundreds of dollars just to diagnose and with no guarantee they will find anything. Has anyone run into this problem before?