Yeah, like 2dark said, neon or fluorescent lights are usually pretty bad. Also, dimmers are notorious... where I used to live, we had dimmers downstairs, and even recording upstairs on the other side of the house, the noise made all my recordings unusable when the light with the dimmer was on. Also check for ground loops... if you have to plug your gear into more than one outlet, each outlet might be grounded slightly differently or on a different phase of your wiring; the bottom line is that voltage differential can be created between two different grounds, and if two different grounds are connected by your gear wiring (such as through the cable connecting your pedalboard to your computer), that voltage differential can create a nasty buzz or hum. Try bypassing one cable or piece of gear at a time until the noise goes away. If you get just as much noise plugging your guitar straight into your computer and bypassing your pedalboard, then you probably don't have a ground loop. Hope that helps!