We recently moved into our new house and I've started to notice a high pitched whine coming from the furnace. The house has 2 zones, and I only notice the whine when zone 2 (the 2nd floor) of the house is heated. There is no whine when zone 1 is heated. The furnace is a Lennox G61MPV gas furnace with a variable speed blower.
I had the HVAC installer come out this morning to take a look. He verified that the whine only happens when heating zone 2 and when the blower kicks up to its highest speed. He said that the reason I don't hear it for zone 1 was that the blower doesn't have to run as fast since the air is only going to the first floor. He examined the blower, tested the amps output, and observed the fan wheel and everything seems to be operating correctly so he can't replace the blower since there is nothing technically wrong with it. I'm a bit frustrated since I believe it shouldn't make that noise at high speed. They are going to follow up but he said that it could be an airflow issue for zone 2 and that they may need to replace some vents with grills to increase air flow in zone 2.
Any thoughts or advice would be great! Thanks.