Hi,
I have a ~10yr old Newmac oil furnace (NL2) which intermittently makes a sort of "sucking" sound when the furnace motor (not blower) is on. It doesn't happen all the time, nor does it only happen after a cold oil delivery (I live in Vermont). The furnace is in the middle of an unheated (though not uncomfortably cold) basement and the oil tank is along a wall. The basement is below grade and the furnace otherwise seems to be well-behaved.

I realize that describing a sound is difficult. And, of course, the motor sounded fine when I had a serviceman come by. Since then, however, I have managed to make an audio recording of the noise. A 15 second clip is posted here :
http://www.considine.net/mac/furn_15secs.mp3
(sorry for the ambient noise level).

Has anyone heard anything like this before and/or do they have any suggestions as to what it indicates? The motor that seems to be generating the sound is a Beckett "AFG" model a Honeywell ignition and something by "Carlin" also attached. An image is here :
http://www.considine.net/mac/furnace.jpg

The only thing I have noticed is that the motor housing (the dark section underneath the Honeywell ignition on the right) seems to get pretty warm.

Any thoughts would be appreciated.
Thanks in advance.
Matt

Watch the flame for any slight change during the noise. This will make sure the oil pump is not the noise maker.

Check the oil to motor cupling to see if it is worn or loose. If it is the replacement type/universal cupling King design take it apart and look at where the end caps are for wear.