Thanks for the suggestions.

I jacked up the wheels and gave them a good shake and didn't detect any looseness in the bearings, but I'll have the mechanic double check.

I did recently get a new tire installed so I guess it's possible that it has some sort of defect. How do you detect tire damage or defect not visible from outside? The front tires are slightly different age, as I purchased a pair 6 months ago, and then about 4 months later, I picked up a piece of metal too close to the sidewall to patch, so I bought an identical tire and put it on. The age difference definitely shouldn't cause this type of vibration though.

Wheels should be ok. Aluminum alloys with no sign of damage other than normal wear and tear.

I'll have him check the suspension components. I know I need new sway bar bushings and end links (bad roads here wear them out) but I don't think they're so terrible that they would cause this type of vibration, especially in a fixed speed range.

As mentioned in original post, lug nuts were checked and are nice and tight.

I don't think the struts are the problem as I just replaced the struts six months ago due to one being broken at the top where they mount to the chassis. Perhaps if there's a loose bolt from that job.

Thanks again for all the suggestions. Several there I hadn't considered yet. Part of the problem is that I have no idea when it started, because here in the city, I literally NEVER get above 45mph, so I wouldn't have ever felt it. We took a little road trip down to the beach this weekend and it was freaking me out a little bit the whole way there and back.