1997 Chevy Astro Vibration starting at 40 mi/hr.

I'm trying to troubleshoot a vibration that has recently started with my 97 Astro. The vibration starts at around 40 mph. I've checked tire pressure, lug nuts, and tires for bulges and all are fine. I recall having a classic Volvo some years ago, that developed a similar condition, which turned out to be the driveline support bearing. I was able to fix that. I'm wondering if this should be the next place I look to correct the problem or if there could be other conditions going on? If there is a strong possiblility that this is the problem, can the work be done by a home mechanic?

Thanks alot,

sgreen7