If he's been napping there consistently in the past, it might just be a phase, teething, etc. You could certainly ask about the white noise machine in a nice, non-offensive way, if you think it would help.
My first step would be to simply ask the providers if they have any ideas when he hasn't been napping. I'd approach it as a collaborative situation and see if they have any suggestions for you or to help remedy the situation. It's probably just a fluke and he will start napping again, so I wouldn't jump to conclusions that they need to do something differently, but I'd ask instead. Maybe they have a suggestion for you or would really appreciate the white noise option.