About a month ago, I replaced my old furnace and A/C with a new 5 ton air conditioner and furnace installed with a furnace-mounted media filter. In the beginning, the motor was very quiet. However, I have started hearing a high pitched noise when the unit is running as well as some noises when the motor and blower wheel are getting close to stopping. The furnace is in a closet. The furnace has a variable speed motor and is rated for a maximum static pressure of .8 in. w.c. I have just found out that my new system has a static pressure of approximately 1.0 in. w.c. which is about 25% over the maximum rated for the system. What could be some reasons for why the noises have started? Could the excessive pressure be causing the motor to start being noisy? What kinds of problems show up when a variable speed motor is operated above the maximum static pressure? Any input would be appreciated.