Automotive A/C heater blower motors are not insubstantial motors and I would not be at all surprised if one could draw 11A. Stall current could be much greater.
To simply speed control this, PWM going to be your best bet. You should be looking for a motor driver than can handle above 11A -- there are some Pololu parts that are sized for this and that aren't too expensive. Making something out of discrete MOSFETs would be the simplest and cheapest, if all you want is speed and not direction control.
It is possible to change the PWM frequency. Depending on the driver you pick, there may be limits to what would work well. Also the frequencies available depend on the PWM pins and are available in possibly inconvenient steps. Have a look at this playground item: http://arduino.cc/playground/Code/PwmFrequency
and also do some forum searches, also on the old forum, to see what discussion has gone before.
Personally, I would not get too hung up on the actual frequency of the PWM. Get things going with the default frequency, which I think is something like 500 Hz, and see if you can live with the whine. If it bothers you too much, then by all means mess with it.