I have my 996xt connected to my computer on a full-time basis. I use a null modem cable from the rear serial port connected to a serial-to-USB adapter cable. For the past couple of months, I have been experiencing interference on a particular VHF frequency for my local PD, 156.090. That interference is present on the 996xt, my Icom IC-R5, and my old Uniden BC-890, where the squelch remains open on that frequency as a result (no CTCSS). In attempting to locate the source through trial and error, I found that the serial-to-USB adapter is the source of the interference. When I disconnect the adapter from the computer, the interference stops. When I disable the adapter in Device Manager, the interference stops. So, has anyone else ever experienced this before? Can anyone suggest any solutions to this?