The weird thing was that whenever the printer arose from a slumber, my lights would flicker and my UPS' would kick in. Checking the UPS logs, they had to switch to battery due to "line noise." A bad AC sine was usually an indication of a bad ground, so I took a look at the printers undercarriage with my handy multimeter. There were a lot of chassis ground connects, but they all were grounded correctly. Cable seemed to be grounded correctly, too.
I contacted Brother's support group, and here's the response I got back:
Dear Brother Customer,
Description of Symptom:19266
The lights in my room flicker when the printer is warming up or
Description of Solution 500000025996
HL2040 PS QZ01 Lights flickering or dimming when using the printer can
be explained by the following information. The average operating
currentfor the printer, as determined by Underwriters Laboratory (UL)
testing is 8.6 amps. However, when the fuser is cold or when the printer
is warming up, it will jump to 40-42 amps. This is a design element to
enable the printer to get ready for a quick time to first print. The
power spikes up to ready the printer quickly. Sometimes the spikes will
cause lights to flicker as the power is drawn.
The printer has been tested and approved by UL. The printer will not
damage home wiring. UL has confirmed that the home circuit breaker
wouldtrip before any damage would occur. This design element ensures the
printer performs 20 pages per minute printing and fast wake up time.
This design cannot be altered and is not an indication of a
manufacturing defect. We do recommend not to share the same power
circuit with other high-power appliances, particularly an air
conditioner, copier, shredder and so on.
Note the copy-and-paste from a knowledgebase. I'm guessing they get several e-mails about that. A 42 amp jump seems to be enough to stress the circuit in the room... so I guess I'll just have to be glad I have a UPS to protect me when the printer eats my AC.