I used to play music a lot using my iphone connected to an NAD amp and Q acoustics speakers with a phono to 3.5mm adaptor cable. A few months ago i started getting a rhythmic, bass clicking noise, like a heart beat through the speakers as soon as i connected the iphone, its gets louder or quieter depending on the amp volume but changing the iphone volume does nothing. Music will still play but the clicking noise is there all the time in the background. I dont get this when I plug headphones into the iphone and if I plug a portable cd player into the amp using the same cable I also dont get this click. Its obviously the iphone doing this, but im not sure why or how to stop it?