Mine's like a woman - sometime it moans constantly and for no apparent reason, other times it doesn't moan for weeks. I don't think it would be the power steering pump, and it would only make a noise when you're turning.
I think mine is my clutch or thrust bearing - i will get round to changing it one of these days and let you know if it helps.
Mine appears most regularly around 4000rpm and sounds like: a balloon releasing air really fast, or a cat trapped in my glovebox and meowing really loudly and passionately. It drives me nuts sometimes!
: Red.dot discs (F), Ferodo pads, thermostat, front wishbones, condenser, MAF, Brembo discs (R), Falken tyres
"Because Alfas have flaws, they feel human, as if they have a soul and a temper. Each one — is like the tortured hero of a Russian novel, a car you can never truly fathom, especially when it is 4 in the morning and it is enveloped in a cloud of steam, yet again, on the North Circular."