I have built a pergola on my own about 1.5 years ago and it doesn't stop making those cracking wood noises (like the wood is cracking).
First of all I know I have built the pergola pretty good because I have followed the instruction of a friend who owns a wood business, and the pergola also "passed the test" of a very bad weather with very strong wind and rain this winter. I examined the pergola and I couldn't see any cracks or broken wood anywhere.
There are 2 kind of noises that I hear, I assume that 1 of the noises comes from the material that lays on top of the wooden pergola, while the other noise comes from the wood itself.
The noises comes mostly when there is a change in the weather, the noises start when the sun comes out and last for about few minutes, they start again when the sun goes away, and so on every day.
At first I assumed its because the wood is new, and I know wood tend to expand and shrink depending the weather, moist and such, but I thought that after a year it would stop, but it doesn't, the noises sounds the same.
I figured the noises come from the small wood bars that lay on top of the "main" frame and not from the frame itself, those wood bars are there just so there would be less sun inside and not for holding the structure together, when we put them on, they were not straight enough, so we had to manually put them in the right place with force to be straight, and I assume because of this I hear the crack sounds because they are trying to bend back to their first form.
Should I be worried? How can I check if I should be worried or not? While I can't see any big cracks in the wood I know that in most cases it doesn't matter and the wood can break without notice anyway.
How can I stop it? Is there anything I can do to stop those noises? It happens on a daily basis and it is something that really starts to bother me.