The same thing happened with my GF Marlin. I took it in to my LBS, he tightened the cranks, and the creaks were completely gone....for about 75 miles. There not as bad as before, but I tried to tighten the cranks myself and it didn't work like it did at the LBS. There he tightened the cranks a good 3-5 turns and it didn't look like he tried very hard. When I did it I had to try hard and I could barely tighten it at all. I hope you find out what to do so I can find out too.