That really does sound like a balance problem. By any chance does it come and go every few seconds? My wife's Subie has had a problem with 3 sets of tires where they appear to get slightly out of balance after a period of time, and then it a vibration comes and goes - but you can only feel it on a very smooth road. And the coming and going appear to be two slightly different sized tires getting in phase and out of phase. If you get it on a surface that isn't smooth you normally won't feel it. And it doesn't follow a particular tire as I can rotate them and still have it.

One set of tires was replaced under warranty and that fixed it - for about 5,000 miles. Then it came back but only on really smooth roads, meaning a very smooth surface texture as well as no bumps. Get on a road with a rough texture or small bumps and it'll go away. We wore those tires out with the vibe and then it went away with the next set, a different brand, only to come back after 30,000 miles. I still don't know what the deal is.

 

Nope the vibration is constant until I get below 60 and then smooths out.

When I take it to the tire shop Friday I'll ask for the high speed balance and alignment.

 

I'd jacked the front end up, set a big socket within a 1/8" from the sidewall on the tire and spin it. See if it spins true. Then put the socket forward of tire, close to the tread and spin it. It really sounds like an out-of-balance tire, but it could be that the wheel is not centered perfectly on the hub. Is there any play in your bearings?

 

Nope, no play in the bearings. I checked them again last weekend.

I'll try your suggestion tonight if I get home soon enough.

 

As dumb as it sounds had a vibration similar to what your talking about chased my tail trying to find as you are..
What I found was the bushes in the rear leaf springs flogged out, causing all the problems..

 

I'll check those out too. thanks.

 

Back for the update, sorry it took so long. Wheel balance and alignment did no good.

BUT, I found the problem. The spindle nut was stripped. I know, I'm suppose to replace the nut when I replace the bearings. I didn't. I was lazy and it cost me. Could have been bad too so lesson learned. Thanks everyone for your help and suggestions.