Just looking for off the top of your head suggestions. I've yet to take anything apart.

A hrrrrrrr sound. Constant without change in pitch or tone after the first h. Intermittent, it might occur twice in the 30 minute drive with each episode lasting at least three seconds and as long as eight. It appears to come from the front left of the car but that could be entirely misleading. Occurs regardless of temperature or precipitation.

The car is an E420 with 145,000 miles. The rear subframe came out last year for a job and all the rubber bits (along with the multilink) were replaced. That is not true of the front.