Equipment faults have to approached systematically... if you assume that's it's the pre-amp you're entering a world of pain and expense.
So before you do that, it might be a good idea to plug in a different microphone and to use some different cables.
It's just that cracking sounds and hiss combined sounds like a dodgy cable and or a dodgy mic... or a loose connection.
The trick is to look at all the elements involved and then rule out as many as possible using basic scientific methodology.
So, you need another mic, another cable and another camera... you plug the new mic and cable into your camera and if the problem goes away you know it's your mic or cable. You then take your mic and the cable you know is OK and plug it into you camera... if that's OK, you then know it's the original cable.
A cable is always the most likely problem because it gets more abuse as is the most fragile.