Noise from machine

My machine has developed a hum. What would be the cause of this? It is just enough to annoy me and I must turn on a noisy fan to not hear it. Also my husband hears it. Any suggestions. It begins as soon as I start breathing and I have changed all filters hoses etc.

Seeing as you didn't identify the machine, it might be a good idea to ask the company where you got it if they have any ideas.