I've not slept well these past few days. Late nights fuelled by coffee and wine have left me too wired - sometimes the caffeine and the alcohol do not balance out, instead aggravating each other. My friends know I think too much, and they know (and I admit) that I live too much of my life inside my head. So at times like these I ruminate on my faults and chew over issues that should have been slaughtered decades ago. As usual I reach no conclusion.

That's what keeps me awake - until something occurs elsewhere in my life that makes me forget.

But during recent nights there's been another nuisance too. A distant periodic hum that's annoyed me even more, stopping me from sleeping. Last night I tracked it down. So let me tell you about my hearing.

My parents were always astonished by my hearing. I've been able to detect sounds that others couldn't: the high-pitched scream of a power supply transformer; the background buzz of a mis-tuned radio, long thought switched-off; the whisper-quiet hum of a hard drive; televisions switched on in other houses, and worst of all, the nightmarish ticking of clocks. I cannot sleep near an analog clock - even the smallest, most insignificant ones irritate me. Watches too.

I've been to gigs, all-night concerts and for two years worked near an airport. I've felt the throbbing bass-lines of The Wolfgang Press shake my stomach, my eardrums responding similarly; I've witnessed the majesty of Band of Susans' guitar drones, of My Bloody Valentine gig climaxes, Orbital at the Royal Albert Hall and the exuberance of Sonic Youth. Throughout all of this, my hearing remained intact.

Then a few years ago I noticed a slight worsening of hearing in my right ear, and when it didn't improve after a couple of weeks I had two full hearing tests. The conclusion that came back both times was that, compared to the general population it was considerably better than average. My left ear, just slightly better. Completely unintuitive, I know, but nothing to worry about, apparently.

At 3am last night, convinced that the hum wasn't coming from another house, or from across the river, I stealthily wandered around my house looking for a source of the hum. I thought it might be the freezer or refrigerator - two prime candidates - but no. Our main computer server burbles like a tiny water cooler, and I can put up with its behavioural vagaries. That too was not the origin. No, it was the fan in my Mac Mini, parked on top of two hard drives, sat on a shelf screwed to a wall in my office. A full twenty-five feet away from me, through two doors and/or two fitted wardrobes and another wall. Usually shut down automatically at 11.30pm, it kept itself awake for some reason, so I forceably turned it off and peace returned to my head.

Thereafter I slept, and for the first time in many days I dreamed. And I dreamt of teeth. Typical - even when asleep I can't stop thinking.