The humming sound is the fuel pump. this is normal the sound is the air compressor for the ELC (Electroinc level control) it pumps air into the rear struts the level the car out when you turn on the key.
Possibly worn wheel bearings can create a humming or groaning sound.
A bearing going bad.
If the car is straight drive check the transmission fluid for full. Check the u joints on a rear wheel drive. Look for any loose parts on the exhaust system as well to try and find the humming problem.
You may need differential fluid...check that.
A humming bird
No, but a bad wheel bearing could.
Where is the humming located front, rear? Could be a vaccuum leak if high pitched, wheel bearings, improper brake installation. More info needed.
Replace universal joint on rear of driveshaft
It may need new brake calipers.
The motor which blows air through the vents.
Check transmission fluid and power steering fluid.