Bing, given your location and the current season I would guess you have a bat colony living somewhere within the structure. I dealt with this last year, wasn't cheap. I was going to handle it myself but bats can gain entry in gaps as small as ~1/2" and I wanted to ensure they were gone for good so I used a wildlife control service. Because they (bats) had already setup shop in my attic they were more likely to search hard for another gap if I wasn't careful to fill them all.

Their process:
Seal all gaps exceeding 3/8" in size (lots of caulk)
Find the most likely spot of entry. Should find guano and a brown greasy film around the spot.
Put a tube or netting on the outside of the hole.
This should be completed prior to the temp reaching 50F
When temps consistently reach 55F (likely April/May) the tube/netting can be removed and the final hole sealed.

The process for bat control is called bat exclusion, tons of info on the Web. I believe many states have laws against killing bats so I would proceed carefully (or quietly) to avoid trouble. I did a lot of research on this and talked extensively with the dude that took care of it for me, can try to answer any questions you have based on what I learned. Good luck.