If you haven't already, make sure you change your Linksys from the default
settings:
- for the passwword at the setup page
- for the channel used for the connection

There may be another access point - a neighbor - using the same channel for
access. Users tend not to change the channel setting - "1" is the default.

There are also cordless phones in the same frequency range.

Your problem with the baby monitor could also be interference from another
monitor nearby, or a cordless phone. Anyone move in next store recently?

I have also seen reports from some radio hobbyists of interference from Linksys
power supplies to radio equipment. Some of the newer Linksys power supplies
have a filter in-line.

I have an 802.11b wireless network in my house; the access point is a
Linksys DWL-1000AP. I also have a pair of baby monitors, made by Safety 1st.

I suddenly noticed considerable degradation in the performance of both of
these devices. They continue to work, but the network connection is very
spotty, and the baby monitor has lots of noise.