Oldsmobile/Buick Repair: Car Shaking, aftermarket custom wheels, olds alero

Question
I have a 2001 Olds Alero with approximately 52,000 miles on it.  For the past few months, I have noticed the steering wheel shakes in excess of speeds above 50 mph.  I recently got four new tires and had them all aligned and that didn't solve the problem.  What could be causing this?

Answer
Hi,Amy.
 A few things could be causing this,ive seen many on the Alero,and ill try to summerize the main causes and fixes,though its hard for me to fully diagnose without driving the car and doing my checks ill try the best i can in what ive found.
 What i need to find out is,are the wheels you have aftermarket/custom wheels?or do you have the stock wheels?if you have the stock wheels,are they the steel ones or the Aluminum ones?the stock steel are black and have the hubcap installed,if you have the stock steel wheels,GM issued a PI {internal bulliten,usually only the tech engineers can access}back in 2002-2003 about the Alero steel wheels,they stated that they had complaints about tire/wheel shimmy or vibration at speeds,and what they found was the steel wheel that was built between 2000-2002 were defective in that they had to much lateral runout,in other words they were bent from the manufacturer,they had a code stamped in the wheel it started with a letter Z,and the fix was to replace the steel wheel.this would elliminate the vibration.
Now if the wheels you have are aftermarket or the factory aluminum then i would have the tires and wheels rebalanced but what is known as forced balanced,alot of the tire places should have a force balancer,usually they dont use the machine when you get new tires because it takes to much time to do,they want you in and out fast so they just spin balance,a force balancer is a machine that balances the tire and wheel as if it has the load and wieght of the car on it at 50mph,this corrects any out of balance that the complete wheel and tire has,the alero is a very tight suspension running car,meaning you can feel everything in the road including tire shimmy.Let me know what tire/wheel combination you have and ill give you a better diagnosis.
 Also have the ft suspension checked for worn out items,mainly the outside tie rod ends,and the ft Hub Bearings,ive replaced many Hub Bearings/ft wheel bearings on the Alero for a vibration at speeds and shimmy.
 Let me know what you find,and feel free to contact me with anymore help.Thanks

ED