Our storm drains. I'm positive there's a break somewhere because when I rains a lot our sump works overtime. The basement has flooded twice because the sump failed and there was a 7 hour power outage. No one else on the street has the problem.
Next year (It's too late now) I'm going to buy a waterproof camera and fish-tape from ebay, hook it up to the laptop and see what I can see.
Also, Bradford pear trees. They are a royal PITA. We have two that provide nice shade during the summer but because of their size, they're weak and are starting to drop limbs, big ones. Plus, their leaves don't completely drop until late December, so it's snowed and snowing and these bastards are still dropping their leaves.