We have central air and turned on the airconditioner yesterday. Before we went to bed I noticed a lot of water on the basement floor and traced it to the pvc pipe that connects to the base of the April air humidifier and goes over to the drain. It was overflowing. We had previously changed the filter and poured vinegar in the pipe and plugged the end for a couple days to break up any hard minerals. After a couple days, we unplugged it and ran water threw with no problem. So wondering why water it is overflowing. We shut the water supply off until we figure it out but the house is now dry. Then woke up to 2nd problem this morning. It started to make a loud noise (not sure I'd call it trainlike) but loud. I turned the thermostat to off thinking it would shut off but it continued to make noise for another 5 min. I was afraid to leave it running so not knowing how else to turn it off I hit the furnace with my hand. I know what you're thinking... it was more like a smack. A couple smacks and it shut off. What would cause that?

The only thing I could think of what would cause this noise and water is that the combustion unit may be hitting the fly wheel on the crank shaft. But then again its hard to say with out all the information about your hvac system.