Does sound like intereference. What happens when their laptop is turned off ?
What version of OS X are you running ? Is it all up to date on software updates ?
What WiFI router do you have ? Is it all up to date on software updates ?
A 2011 MacBook should be somwhat better than its predecessors as Apple put a new WiFi chipset into there alongside a new RF design.
Last edited by mixture; 20th March 2013 at 23:27.