The first thing to do is check that all cables are in good order and are not damaged. Try different sources with the Penta to rule out that it may be the signal source which is causing the noise. Also eliminate the receiving device being the problem by feeding the Penta signal to different receiving devicess to see if you can still hear the noise.
If, after testing the above, you still think the noise is originating inside the unit, please test the following and contact us for further support:
Does the noise occur when using the mic and line and instrument inputs?
Does the noise occur only when the compressor is switched in?
Does the noise occur when only the width control is switched in?