Time Capsule makes iphone clicking noise when spinning up

Hi

Every time my time capsule spins up it makes a sound which is identical to what you get when you swipe your finger to unlock your iphone.

The time capsule is in my living room to maximise airport coverage throughout the house and the clicking is getting a bit annoying - the actual disk operation is near silent.

1. Is this click-on-spin-up a standard feature to all time capsules (hope so!)

2. Any way to switch it off - I can't see anything on my mac's Airport utility?

This is definitley not a hard disk sound - it sounds exactly like a sythesized iphone unlock click

Thanks

Jon.