Thank you for your quesiton, I'm Dr. Dan and I'll try to help you.
I think at this point we just need to be watchful. Whistling while breathing is concerning but we need more evidence before we go to the vet. If he continues to whistle for the next couple of days, or his eating, pooping and "acting fine" change at all that is another reason to see the vet. Not every episode of whistling or wheezing is a medical problem. That being said consistent whistling or additional symptoms are worrying and a vet needs to be seen as soon as possible. I hope this helps, if not please feel free to ask more questions, if it did help, please leave a rating. Dr. Dan
The dehumidifier is fine, I recommend treaments like that for mild respiratory problems. If you are concerned, try turning it off for 36 hours and see if it goes away. Most of the time unless the dehumidifier is really old and moldy, it's not the source of the problem. Most likely the stress of transferring to a new home would be culprit if this get's any worse.