Impreza vibration at 69mph

[Xavo]

My 2003 Impreza Outback Sport automatic starts to vibrate ...just
slightly... approaching 70mph. The vibration is cyclical: it lasts for about
3 seconds, then stops for about 2 seconds, then vibrates again for another 3
seconds, and so on. I can feel it in the steering wheel. I had a wheel
alignment done but the vibration is still there. It has happened on three or
four different highways and road surfaces. The A/C is off.
What causes such a cyclical vibration?
Thanks
Xavo

 

[jabario]

tire balance is the cheapest and easiest to check for

 

[Carl 1 Lucky Texan]

exactly, also tire tread seperation. Even if they balance, they can have
problems - particularly tires older than 5-6 years, regardless of tread
depth/wear.

Carl

 

[Greg]

1st: Wheel alignment will not cause vibration.
2nd: As noted in the responses, check balance and wear. Worn tires can cause
road surface related noise and vibration even if they are in "balance".

 

[clintpatty]

This isn't an answer, but I have the same vehicle (year and all) and don't
have that problem. Do you hear a special engine sound @ like 62-65mph?
Also, what mileage do you get?