Whilst charging from an ACP-12X mains charger, I noticed a high pitched whining / whistling sound emanating from the legacy-charger to MicroUSB adapter thingy that comes (bundled with the n900 to enable it to work with older chargers....(NOT the charger)...which alarmed me especially as I'm in the office surrounded by iphone sheep.....

Sounded like the pitch was increasing so I unplugged it straight away. Not sure how old the charger is.....

Was charging OK up to now - Should i be concerned ?

Known "issue". Others have reported the same hissing from the adapter, but without ill effects (even though it's scary).

In fact mine also did the whining, for a while (especially when the device is completely charged), and a few days after it stopped...

Many power supplies make whining noises (vibrating transformer) or hissing noises (not sure what causes this but it's quite common).

If you don't smell anything burning there's probably nothing to worry about.

The adapter brick is a DC/DC converter that makes sure the USB port sees 5 volts as required in the standard, while the older chargers the adapter is intended for use with can give out anything from 7 volts to nominally 5 volts, really like 6,3 volts - or something quite different, the old battery system wasn't that picky.

As an average high-efficiency stepdown DC/DC converter works in buck mode, i.e. switching the voltage on and off rapidly (tens of kHz or preferably more) - to step down just a bit, keep the voltage ON for much longer than OFF and you get a drop in output without significantly wasting power to resistive losses - and filtering the output, it's perfectly possible for the swithing process to produce audible noise. The noise is usually a sign of somewhat lazy design - it's quite easy to make sure the possible noise does not fall into the range picked up by human ears (and higher frequencies usually mean better efficiency too), but even with the best design there will always be some units in large lots that are always noisy due to e.g. component tolerances. Usually if a new unit is whistling, this is not a reason for greater concern, but if an old unit suddenly starts doing it, it is most likely dying and needs to be replaced quickly.

Changes in whistle pitch (in this case) are indicative of changes in charge current - the brick I'm using is almost perfectly silent when the device draws full current, but when the battery gets fuller it starts to whistle, gently at first and finally slowly chirping quite audibly when the charging is finished. Funny thing is that the chirping seems to be indicative of GSM/WCDMA and CPU power draw cycles - when e.g. scrolling the image gallery, the pitch is reduced considerably and when the scrolling stops, the pitch rises again (CPU working, drawing power vs almost no load and very low power).

could be "coil whine". I doubt it's capacitor leakage based on the description, but if so that would be bad.

Thanks all for your re-assurance. No noise today - it seems fine now.

Regards,
Sam

Anything we know? Perhaps its just happy?

Yeah, mine often makes that noise, and if I'm in a quiet environment, I can hear rapidly varying "activity sounds" from the adapter according to N900 activity too.

Here you go.

Anyone esle notice this? High pictch scream or singing when charging. At first i though it was coming from my N900 but no it is the adapter.

It tends to sing when it is hot, and presumably doing more work. Once the battery is close to full the singing stops.
Just a little quirk i presume.