The AC guy noticed that our dryer vent, which vents off the roof, had become detached when they put the second AC intake vent in. Thank God he told me about it. The dryer vent guy came out and we found out why the vent stack had become detached, it was the weight of the lint build up. He said on a scale from 1-10 for a fire hazard it was a 15.
I guess there is a learning curve to owning a home. I have never heard of cleaning out the dryer vent, but then again I grew up used to basements with laundry rooms that vent out the foundation, not straight up.