The tap test is when you *gently* tap on the egg and wait for a response. I know a lot of people don't do this until they are internally pipped and listen for an answering cheep, but I do it before that, and feel for a vibration as the chick moves in response. Hens and chicks communicate...
No peeping or anything?? Did you try the tap test? What day is this for them? I do know that incubator cleanliness is very important, but I hope you at least get one or two!