It's not uncommon for the boats to creak and groan occasionally, but generally speaking, loud cracking sounds are not good. I would give the whole boat a thorough inspection (not just the mast base area because occasionally sounds have a tendency to come from somewhere other than where you think you heard them).
If your dolphin striker is loose, it could have been your front crossbar cracking, so I'd give the crossbar a real good inspection (maybe even remove it from the boat). Also check the crossbar anchor points and shroud anchor points on the hulls, check the mast and rudder connection points. A loud cracking sound is a warning that there is a part somewhere that is probably getting ready to fail.