Lot of cracking noises in the attic
They could simply be thermal expansion and contraction, delayed due to the large heat capacity of a home. It takes quite a while for the solar gain that has soaked into an attic to be released, for example. 

I'd stake out your attic Columbo-style and give it a good listen and feel. Chances are it's not a sign of structural problems, but it's surely an annoyance.