C.E.
Hi C.,
I had the same problem because my 2 girls are in the same room, but my boys are 1 & 2yrs old and need to be in separate rooms so they don't wake each other up.
The only solution we've found was to buy 2 of the Fisher-Price Private Connection Dual Monitors. They each come with 1 base unit and 2 recievers which is great because I can have one in the kitchen and one in my office and be able to hear both of the boys if they are sleeping at the same time. They are on separate channels and we don't get any static or interference from it.
They have them on Target.com and they are $52/each, but well worth it!
Hope this helps.