I'm at my wits end here.

I have two identical rapid start 2 lamp 4 foot T12 fixtures in my
bathroom both of which are about a year old. One buzzes and always
has; the other is silent. I want to install a new fluorescent fixture
in the kitchen but SWMBO says not if it buzzes and points to the
bathroom fixture and my inability to stop its buzzing. Since this
isn't the first fixture that buzzed she points out that obviously
fluorescent lights are not yet ready for prime time. Unfortunately I
have to agree with her but in a last ditch effort to prove that it's
mere accident and not the innate incompetence of the manufacturers I'm
trying to get the bathroom buzzer to stop.

Both lights are on the same circuit wired through one switch. The
hot/black is the wire interrupted and is correctly connected to the
black from the ballast in each. When the switch is off neither white
nor black carry any current. The white is correctly connected to the
white of the ballast. I've checked and re-checked all electrical
connections. Both fixtures and hence the ballasts are grounded
properly. I've swapped the lamps from the non-buzzer to the buzzer. No
effect; the buzzer still buzzes. I've replaced the lamps in the buzzer
with new ones. It still buzzes. Since the buzzing seems to come from
the ballast, I bought and installed a new ballast (same size for T12
40 W); the new ballast buzzes just the same as the original.

I'm not sure if this has any relevance but if I remove both lamps
(with the switch on) the buzzing stops. If I then install one lamp
there's no buzzing but the lamp doesn't light. If I then install the
second lamp both lamps light and the ballast buzzes.

Someone must have some ideas...