Hafler DH 110 grounding inputs and signals

DIY, Need some help. I have a Hafler DH 110. Here is the problem. The selector switch grounds all inputs not selected. So, when I select tuner the CD/AUX is grounded and vice versa. Here is the problem. When I have a signal going into the tuner and then select the CD/AUX, Tape 1 or Tape , there is a faint signal that can be heard. I was under the impression that grouneded inputs meant dead silence. I checked he manual and it tells me how to make sure the outputs are functioning. I also checked each output as I turned the selector switch and sure enough they are grounded. I cannot figure out where the extraneous signal is coming from. I have attached the schematic for reference. Any ideas or troubleshooting help would be appreciated. And if this is normal behavior for this preamp that's okay too. My APT Holman does not do this. Thanks again. Mark
 

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