This is a known problem with the Creative 6700 speakers. A faulty power supply when they 1st came out meant that Creative had to replace either the power supply adapter &/or subwoofer on all of the first customers. The power supply was damaging the sub & cutting in & out, hence the loud popping.
Creative were happy to send out the replacements to all customers who logged the problem with themn via their web-site - I had a new sub & a new power supply adapter & this fixed the problem. I will look up the details & post them soon. Hopefully they can sort you out very quickly. This problem was affecting so many customer that at one stage it looked like they were going to have a riot on their hands, but they were very fast in sorting it all out & keeping everyone happy.