Could you try to get him to sleep at home in lighter condition, and play some background noise like the telly, maybe he manages. I don't really know, but if i was in your case, this is what I would do.
When I take Lucie to my sister's house for the weekend she does not have a black out and she lives on a main road in Manchester, very noisy. Lucie takes longer to settle but manages to sleep, if she does not get enough I always make sure she gets quiet time with DH or me, just looking at books or bilding blocks. Maybe the nursery staff can do that with your lo too, if she does not get her normal nap times.
Is it posible for you to be in the nursery for his naps in the settleling in sessions?
all the best