The speed of the blower is critical to correct operation of the unit. If you try to slow it down it could result in overheating and damage to the exchanger. The noise is probably related to something else other than the motor speed. Have the installer check it out.

Yes, I agreed. you should have to recheck the your gas furnace. It has an error.
Good luck!!!
______________________
gas water heater

If you have an older furnace, and are buying an older home- especially wanting to save money - there is a GREAT FHA mortgage program- that replaces your outdated system with a brand new one including a warranty. All with no out of pocket costs!!!

Look at this site for information:

http://www.eemdirect.com/