Higgs Boson wrote:

My computer (PC, 5+ years old; well-behaved), has started SCREAMING every few minutes.
It wants something, or is warning me of something.

I just paid a consultant pretty fair bux about two months ago to
upgrade, so I'm tapped out, computer-wise, but
scared to death I might be hearing a death rattle.

Any honest consultant who upgraded your computer just two months ago
will check your computer for free and charge you nothing for minor
repairs.

Stuff that can screech in a computer:

1. Fans -- in the power supply, on the CPU and maybe the graphics
card, in the case. Try stopping each fan momentarily and listen for
changes. Do NOT try to stop the power supply fan by sticking a
screwdriver into it because there's exposed high voltage all over the
interior of the power supply. Instead use a disposable plastic straw
because plastic doesn't conduct electricity, and disposable straws are
flexible and won't break off or break fan blades. Stick the straw(s)
in before turning on the PSU. Replace or relube noisy fans. Relubing
ball bearings usually doesn't help, but a drop of light machine oil
(5-10 weight) can silence sleeve bearings. Sometimes it's not the
bearings but a thrust washer that's screaming because of scoring or
distortion. Real hardware stores sell replacement washers, both metal
and plastic (nylon or delrin).

2. Disk drives -- rarely. If the drive is identified on the BIOS boot-
up screen, it's highly unlikely the drive is screaming.

3. Speakers -- the audio circuitry may pick up noise because of buggy
software or because a filter capacitor is really bad and causing AC to
get into the circuitry's power.

4. Inductors -- coils and transformers in the power supply, on the
mother board, and on most graphics cards. Sometimes their windings
are simply loose, but screaming that suddenly appears often indicates
bad capacitors, which can make transistors (MOSFETs) turn on and off
more gradually or make the output voltage low and cause a voltage
regulator to try too hard to compensate. Bad capacitors aren't
unusual in 5-year-old computers, and in the case of power-hungry
Pentium 4s, even quality brand capacitors. Also one of those quality
brands, Nichicon, had a bad run of HM and HN models from about
2001-2004. See www.BadCaps.net for lots of information about such
problems. Bad caps can eventually make MOSFETs burn out.