Crackles between tracks on Airfoil

Hi there

I'm running WinXP using Airfoil to stream Spotify from my laptop to Airport Express which is connected to my hifi.

When I change track on Spotify my laptop makes a couple of clicks, then for the first few seconds the volume is a lot quieter and there are crackles and clicks coming through the hifi speakers.  After that it plays absolutely fine.  Any idea what the issue is?  If I do similar in iTunes (and hence don't use Airfoil) I have no such problem. 

Any advice appreciated as apart from that I'm really happy with the setup!

many thanks

Gareth