Strange Whistling Noise During Warm Up

[jayjay2cv]

Hi, just a quick question. When my 64 plate 1.6 eHDI is warming up, every so often I can hear a whistling noise which just lasts maybe a couple of seconds and occurs every 10 mins or so. Once it's warmed up the noise disappears. I have also noticed that it does it sometimes when you first unlock it and open the door in the morning.
I'm not too concerned but wondered if it was normal?
Thanks for any help.

[taxi]

Relays ?

[jayjay2cv]

Hi Taxi, that's what I thought especially since it happens when you unlock it a s well.