Hello-
I have a PISMO which works beautifully, except that ever since the charger overheated and died, last Autumn, the laptop makes a loud, steady squealing noise, all the time, unless I run on battery only.

I have replaced:
the PMU/battery board
the AC/Sound card
the hard drive
the combo drive
the AC/charger unit, twice
and then the whole motherboard.

The battery is old, with only about an hour's worth of power left on it (so I keep it plugged in).

I use a new Apple charger now, so it's not a generic one.

I reset the PMU and PRAM over and over again

It's not coming from the speakers.

It's not coming from the screen or the inverter.

From what i can gather, it's coming from the center of the laptop, inside, maybe down where the PMU/battery board sits. (above the trackpad maybe)

It sounds like a photographer's flash unit powering up, only much louder.
Or maybe someone's smoke alarm going off, a few houses down the road.
I always think something is about to explode, because it rises in pitch slowly over time, from high to higher. It confuses the dog. I think he's uncomfortable around it.

I have a new HD, it's silent. I have 10.39 running on it.

If I remove the battery it still squeals, but the pitch drops to a low whine (but still loud).

Mostly I blast music over it (either through the laptop speakers or through another stereo unit in the room).

SO.. I'm guessing an old diode, or capacitor is dying, but where? Maybe the PMU/battery board was the culprit, and the second one I bought on eBay was also bad?

This would be mildly amusing if it weren't such a loud sound (like cell-phone-ringtone-loud).

It's been doing this for three months, so I have no longer any fear that logic-board death is imminent. I think I don't care at all, except that it's such a nice computer and I've put so much money in it.

Let's see.. any other details.. the high pitch drops slightly with each keystroke or click of the mouse, and with battery removal (as I said), and that's about all I can think of.

I think the fan is not the culprit; I've checked it out.

Never are any warnings of any kind given, on the screen, about any software or hardware
malfunction. .

Right now, it's dead-silent. Because I unplugged it. I'll have about forty-five minutes of battery
power, and peace. If you want to know how it sounds, light a fire under your smoke alarm
and then go stand across the street.

Oh, and also, it squeals whether it is turned on or turned off.. it seems to be related only to
being plugged in. At one time, it would stop squealing when it reached 100% charge.
Now, I believe that no longer holds true.
This is the second or third AC/power charger I have tried. (2 generics
and now an Apple unit)

What else can I replace? The PRAM battery? I don't think it's dead. Can a battery make noise?

I've been all over with this question (macrumors.com, macforums, etc) and no one has a clue.

Should I offer a reward?

Can it be in Mexican pesos?


Cheers,
steve

(now I am going to turn it off, plug it back in, and throw a big pile of laundry over, it in order
to muffle the sound)