Creaky Trees?

I felt pretty sorry for Jackson today, as I've been neglecting his excersize.  We found out a few days ago at his annual vet exam that his is now 85 lbs.  So, for all of you that have noticed him getting bigger (ahem, fatter), it is definitely true.  Well, today was rather nice, so I threw the ball for him in our backyard.  Abigail was taking a nap, so I took her intercom outside with me.  Every time the wind blew, I heard an ominous creaking sound.  First, I thought it was coming from the intercom.  Nope.  Maybe the wooden gate at the back of our yard?  Nope, it was still latched and locked.  I then proceeded to check both shed doors as well as glance over at our neighbor's shed to see if they had a flyaway shed door.  No luck.  Could it be the door to the chicken coop two houses down (yes, even though we live 3 minutes from downtown, there are two chicken coops on our street...oh, and a fox that lives at the end of the street that has been known to be the culprit of a chicken massacre awhile back).  Nope, not that either.

Then I decided to look up and realized that the trees in our yard were creaking!  Now, these trees are TALL and oftentimes sway when the wind blows.  This picture doesn't do justice to their height, but you can imagine how tall that tree in the front is compared to the height of the swing.  I've never heard the trees creak before, so if I blog about a tree crashing through the roof of our house tomorrow, you will have been forewarned.