Steering wheel vibration at idle

2005 mercury sable with standard 3.0 vulcan engine. not the 24 valve version. Steering wheel shakes at idle and can be felt in the seats of car. The problem is the electric cooling fan at the radiator. it can be disconected and the problem goes away. Ford Motor co said that is normal, howerver it is very anoying. I have reserached this and found that the plastic blades viberate while they are running. The fans have been changed two times with the same problem. I know they have had this problem for a lot of years, and will not fix it. they have their specs in service manuals set so this is normal. all of the cars do not do this, but some do. the ones that do can not be fixed with the parts Ford motor co. supplies. i obtained one from a wrecking yard and hocked it up with power out of the car, thats when i saw the plastic fan blades shate very much. they are two of these on the cars. this is the right one causing the problem.

Does any one have any experiance with this or have a solution to it. Ford Motor Co. knows about the problem but will not do anything about it. Because they have set their specks in the manual to say this is normal. I am begining to see why the Toyota's are taking over Ford's number two place in sales. The FSB # from Ford is 05-20-08.

any help will be appreciated.