They are pesky little critters.
I have had this problem more times than I care to remember. They are nocturnal and loud as H*ll! The first time I had this problem I couldn't sleep for months until I found the solution.....
And I tried EVERYTHING:
Boarding up the areas
You name it!
etc, etc, etc.........
More squirrels just kept coming back! Even when I killed them, the previous ones had sprayed my attic which attracted others from around the neighborhood...
I agree with David. You do need metal to keep them out. But even if you use wire mesh on the hole, they usually just chew through a different location to get into your attic.
The only squirrel proof solution I have come up with is to aluminum cap ALL your eaves or what ever the item is that they are chewing through.