All of a sudden, it sounded like a jack hammer was placed against the house and I thought someone was trying to break in through the wall. Searched desperately to find where it was coming from which lead to the basement. Turned out to be the furnace. Tried to isolate the problem hoping it might be a DIY. Sound was coming from the vent fan and reverberating throughout the ducting of the house. No wonder it was so loud. Too many wires so I thought better call a professional.
Response was quick and the service well done. However, I felt a bit gouged on the price. Given the severity of the problem they seem to think they can charge what they want. Just the part was $425+. It just a vent fan for Pete's sake. Sheesh! At first I was told it would be a flat rate, and then the billing was change to hourly because the furnace was an older model. What? Since when did a new furnace require emergency repairs? All the emergencies would happen on older equipment, no? The service was done during normal hours too.
Anyhow, furnace was online and emergency resolved. Be prepared to pay big bucks with these guys though :-(