Dogs picking up on this kind of thing is well documented, at least among folk who actually pay attention. My sister had a spaniel that refused to go upstairs for about three weeks before the activity in her flat kicked off properly - we're talking books off shelves, cold spots, the full works.
The knocking is interesting though. Consistent pattern or random? Location matters too. Inside the wall could be pipes but if its moving around thats a different thing entirely.
What's the dog actually doing, cowering or full on growling at a specific spot? Because those are quite different responses and worth noting down. Seriously, start keeping a log right now if you havent already. Timestamps, weather, anything unusual beforehand. You'll thank yourself later when you're trying to work out if there's a pattern.