We rent a house that unfortunately seems to have a crappy electrical
system.  Since it's a rental, we want to invest little or no money
into the problem.  The landlord won't do anything about it because,
well, the house has power... what more is he obligated to provide?

The main problem with the electrical system is that it produces a
ton of line noise and other interference.  I posted a question to
Google Answers a while back about a problem with a bass guitar
amplifier; we thought there might be a problem with the amp, but it
turned out just to be line interference.  I'm having a similar problem
with my computer monitor - every time a major appliance is on (fridge,
microwave, washer, dryer... hell, even the toaster oven), my monitor
starts subtly shaking.  It's very annoying, especially now that it's
summer and it shakes whenever the air conditioner is on.

I have virtually every piece of electronic equipment in the house
plugged into Tripp Lite surge protectors, a brand that I consider
high-quality.  So, my equipment might be safe from surges, but it sure
as heck still gets lots of interference and noise.

So my question is, will a line conditioner/isolation transformer/etc.
do anything for my problem?  They seem to designed to combat
brown-outs and such, but that's not exactly my problem.  Can you tell
me with some detail what my problem might be and what I can do about
it?  Thanks!

Hi  lazytiger-ga,

   You seem to have problem with line regulation.  May be due to all the
appliances sharing the same circuit, under rated utility supply transformer
etc. Typical line conditioners/isolation transformers will not work effectively.
What you need is a constant voltage transformer(also called as ferro resonant
transformer). Sola seems to be a popular brand.
If you would like to share it for a set of appliances on the
same line, you need to break the mains branch at the at a junction box
and wire your cvt to supply from there. Before doing this just make sure
it works by connecting it to a single appliance(such as your monitor).

Hope this helps.

Regards
ldavinci-ga

Thank you, ldavinci, for your comments.  I will do some research on
that.  I forgot to mention in my question that I've also had problems
with grounding.  I've checked several outlets with a simple cicuit
tester and also by using the "grounded" light on my surge protectors. 
The outlets are properly grounded, based on those indicators.  I've
found a couple outlets that weren't wired properly and I fixed them. 
But it hasn't made any difference with the music equipment - there's
still an obvious grounding problem.  If the circuit is "open" (i.e.,
the guitar is plugged in and the amp is on, but you're not touching
anything) there's a very pronounced hum coming from the amp; but if
you touch a metal part on the guitar (most obviously the strings), the
circuit apparently is closed and the humming stops.  I assume this is
somehow related to the other problems I'm having.  Would this CVT you
speak of do anything about the grounding problem?  What would?  Thank
you very much for your help.

Hi lazytiger-ga,

   The problem that you have with the music equipments is due to something
known as ground loop. Ideally you are supposed to have only one grounded
connection(where the "ground" wire meets the real ground/water pipe) for
the entire supply. But if for some reasons you had multiple grounds present,
it is more likely they are also at different potential(unless these grounds
are tied together with a thick high conductive wire), leading to injection
of a low voltage at supply frequency on the ground line. It is more likely
that one of your connected equipment might be providing this "other" real
ground through its grounding pin, leading to multiple ground paths. Firstly
make sure there are no more than a single physical ground(in the form of
ground rods). Then try disconnecting(switching off/tripping the breaker will
not help) each of the major appliances one at a time, while using your amp 
hum for ground loop detection. When the hum stops, you've identified the
culprit providing a "real" ground, other than the one meant for your entire
supply. It is also more likely this is a defective ground thereby providing a
potential difference. You could either disconnect this real ground, or 
improve it by having a physical ground with good conduction(connecting the
ground to a wire, which then terminates in a long grounding rod
(inserted over a moist charcoal/salt mix) outside the residence, and then
connecting this rod to the main grounding rod using a thick heavy gauge wire.

  The constant voltage transformer also provides isolation, which should help
avoid the ground loop problem. You could also try just an isolation transformer
with a grounded metal foil between the primary/secondary, if grounding is the
issue. It will be much cheaper than a cvt.

Regards
ldavinci-ga