In my studio I am using Genelec 1031A with subwoofer. Once I noticed some fine crackle noise within one speaker. I open it up and found some cold solder joints which I could fix. Now all speakers are working fine again. Here are some close-up pictures.
These cracks are quite clear and easy to see, but sometimes the crack is like a hair and you better own a microscope to take a magnified look. Once you spotted the suspect solder joints you should suck of the old solder with a pump before reflow the joint with new, fresh, good solder.