Arduino Shield is noisy with speakers input

Hi there,

i have a Speakers Signal which is very simply. Only in case a button is pressed a signal Needs to be processed (Beep 0.5sec). It is working when Speakers - is connected to Arduino GND and Speakers + is connected to Arduino +. As soon iam starting to use the Shield modul and a Network cable is Plugin in it is not working anymore because it continously blobs a click Sound back to Speakers.

So what to do:

No code, no wiring diagram - we need those...