There are a couple of possibilities- one is benign: they may have just changed temperature and had condensation build, and with the plastic it id still present, whereas with paper towels around them you'd not realyy have noticed- IF that's th cause.
Another cause is bacteria building pressure inside as they reproduce...If that's the case you may already smell it, or they may be slimy. If it's not obvious, I'd just go ahead and put them in, but check every day for any moisture AT ALL. When I've had seepy eggs that were bad, they seeped while resting before incubating, so you may have the answer immediately.
Edit: grammar nazi