I did cleanse and sanitize all bottles with the no rinse sanitizer. But I didn't soak overnight, just soaked long enough to get labels off. I'll be more intense about it this next go round and hopefully won't have an issue. Thanks for the responses.
Brewed my first batch, a standard English ale (Munton's LME) and it's pretty tasty. Most bottles, anyway. Tonight I found my second bottle that has what appears to be mold floating at the top of it. I also notice that the two bottles with the mold seem to be way more carbonated than the ones...