Airport Express with HT Receiver

I'd like to know wether anyone has experienced the following problem: Static/Distortion from speakers. I initially thought that the problem was caused by my using a subwoofer. I'm trying to run APE wirelessly through a Toslink cable into my Denon Receiver's optical input.It's worked before without any problems. Now I've changed speakers and I'm getting this distortion from the speakers.When I play music from CD Player there is no distortion.Any help would be much appreciated.