"howling" when driving. louder as speed increases. Cause? on 2008 Dodge Avenger

Wife's car. I drove it yesterday and noticed a "howling" that started at about 15 mph and gets louder the faster I drove. Transmission "feels" fine when driving. Shifting is good. No noise when idleing or reving up engine. No noise in neutral. Could this be transaxle issue?

2 answers 2 comments
Wheel bearings. Does the intensity and rythym of the noise change or can you hear a difference when swerving left/right at a steady speed?
always check all the wheel bearings first.
Did not think of wheel bearings. I will check those first.
yup. drivers side wheel bearing hub was causing the noise. Went ahead and replaced both fronts. Took less that 90 minutes. Its great to have tools.