Doepfer

On the A-188 BBD 1024 Stage Module, is it normal that it emits a really high pitch sound 
when the delay clock knob is between 1-3. This happens when the output is to the mixer, 
and when nothing or something is plugged into the module itself. It seems to happen only 
when the polarity at the very bottom is either on + or -. Its quite annoying and I was 
wondering if its normal because it doesn't exactly sound that way.
Any response would be amazing.