Noise with krc-86b v4.0 module

Hi, how are you all?

I'm trying to add this bluetooth module to an amplifier. I have a problem with krc-86b v4.0 module | Electronics Forums

I opened a wall phone charger and soldered it to the AC line inside the amplifier so it
can turn on when i turn on the amp, then soldered the module to the 5v charger. Between the AUX input of the amplifier and the Audio Output of the bluetooth module i used a ground isolator.

The thing is that i'm getting this digital noise when the bluetooth is
not in use. The noise gets better when the bluetooth is in use but it's there.

Any ideas of what to do to remove the noise?
 
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