It would have been a self-cleaning furnace!
I had a customer who said there furnace was giving him a headache with a little giggle. I knew something was up.... I get there and his wife was there about to laugh her **** off. There he is with his dust buster sitting on a folding chair down by the furnace. Let me turn it on they both said....no I've seen this before. The gentleman said and you can fix right? Yep, pulled the door, then burners, then the baffles in heat exchanger. So I ask about the headaches, well the lady of the house cracks up laughing and leaves. Well the gentleman says I'm the only one that got a headache from it. I replied I'll test this heat exchanger make sure there are no problems. Well a few seconds later he says if can keep the dirt from coming out that door won't hit me in the head when I'm cleaning around it. Well I lost it.... oh that was funny! So after I start to finish up putting things together, his wife comes back, he makes the comment about how happy he was to provide a good laugh. But he says "I want to what that furnace was doing when it whuumpss on" My reply "it wants to be the 1st self cleaning furnace" I clicked that old Singer/ Afco on just as quiet as can be, he had to stick his nose in there to see. His wife says "watch out for that door" and laughs, covers his head and rolls along the floor..... Needless to say one of the more memorable service calls I had.