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 ?