The cracking sound lake ice makes is very unnerving. Stepping over wide cracks can get the back of the neck hair standing on end as well. What are the possible causes for ice to groan like that?

Kinda unnerving, huh? As long as you're on cold, solid ice in excess of 4" you'll be OK. I notice it mostly on cold days when the temp is below 32. On these days the rumbling is due to the lake making ice. Silver lake has been rumbling and grumbling the last few days while it's gained an inch or two, and it's cracks spiderweb all over the lake. Other days it'll get to talking when the sun hits it, warming it a degree or two. Once again, unnerving but nothing to worry about as long as you're on good ice. The definition of "good ice" varies.....some folks go out on 2". Not me! I wait for at least 4" after several days of sub-freezing temps.

Raffensg64 is quite right, that is a good sound, and it means the ice is expanding. When I was growing up on Rainy Lake N. Minnesota, the lake would boom at night, you could hear it for miles away and inside your houses, not ice house but real house... The lake would get pressure ridges that would lift up 4-6' in places and that is how the pressure from expansion releases. What will make you crap your pants is being on the pressure ridge as it is building before your very eyes. Ice is most dangerous when you hear (nothing)...

That is good to know, about the ice I mean. I want to do just the opposite. Leave when the ice is noisy, stay when quiet. So, clear ice is good ice? What about the white ice with what looks to be air pockets or air bubbles mixed in? looks to be partially melted snow that has frozen.

Yes clear ice is good ice. the more clear it is the better it is. It it a little more spookey since you can see right through it. You are right. White ice has more air bubbles in it. This allows the water to sock through when it starts to melt. Kinda like a slow sponge. Try drilling a hile half way through the ice and the water will slowely seeap through and fill the half drilled hole

The ice at Fish is about 12" now, it's fine, I was there the same day, the ice quit grumbling so much when it cooled after about 11 or noon is when the cold wind hit.