Noise in 2001 camry

I have a 2001 camry. When I had the original tires replaced I noticed a hum. I assumed it was a tire noise, since it only started when I replaced the tires. Tried to live with it until the tires were worn out. It irritated me so much I replaced the tires with a new set that looked like they would run quiet. The tire dealer also assured me he had never had any noise problems with these tires. All four wheel bearings check good. Have taken hub caps off and run it with any, nothing seems to make any difference! Any one ever run in to this before or have any ideas what it could be? Charles