My kitchen sink makes a noise about every 20 minutes like it has air coming up out of water in the drain. I have run my garbage disposal to make sure it is empty and I have poured boiling hot water down both drains to make sure it is cleared. The water drains out of the sink just fine. This is a new sound that I've never heard before. What can I do to stop this? Is it a major concern? We live in town, I don't want some back up into my house.
Thanks for any help!

Do you have a hot water dispenser on your sink?

No, but I wonder if when the refrigerator does it's defrost cycle if that could be causing the noise. By the way, it has stopped making that noise... for about a week now. Thank you for the input, if you have any other imput I appreciate it.

Probably the icemaker filling up. Take the ice out and see if it does it again.