D.K.
I wonder if you have something interfering with the monitor? We have a sound and lights that we have had for a while, so it is probably an older version, but we have the babies room up stairs in a two story house and I take it in the basement and out into the back yard with no problems. Perhaps you have a cordless phone on the same frequecy or a wireless router or something like that?
Good Luck,
D.