I have a Carrier Furnace (Model 58MCA100-16, Series 180, Mfr. Date Mar 2004) that makes an intermittent 'whooping' sound when it comes on and goes off (sometimes but not always, but more often during the late evening and the middle of the night). I had a service technician come out yesterday and after a short time and $98 later) he said he couldn't replicate the noise and that I should keep a log of the 'whooping noise'. My log now shows: 10:34 p.m. 4:04 a.m. 5:34 a.m. 6:07 a.m. 6:21 a.m. 7:45 a.m. --- so, please help. Thank you.