I've built myself a roll around workstation out of a craftsman SS side box with a small desktop pc with surge/battery back up in the botom drawer and mounted it on four casters and have a section of strut bar exiting the top with the monitor and keyboard mounted to it.
I then connected a usb extension(about 3 ft) to the pc and ran it up through the bar to make removal of the pico easier in the event I had to connect to my laptop and do a road test. When I turn on the pico 4423 and have test leads connected, I get a ton of noise as it's set to auto. If I move to the 1 volt or higher it isn't as bad. If I touch the leads together(zero) I get a straight line but with dashes of noise along it. This happens on any channel I happen to have test leads connected to. If I connect the pico directly to the pc(bypassing the extension), it's clean and clear. I then went with a usb 4 port hub with its own external power supply with the same results as the extension.
I'm sensitive to this because about two months ago I was using my pico to show a customer the difference between her newly replaced O2 (from another shop) and the one that actually needed replacing for her original code. That afternoon I went to do vacuum pulls on a no start and when I hooked up my bnc cable to channel B I had all kinds of noise that looked like vacuum pulls, but I had yet to hook up the transducer to the other end. If I disconnected the cable it would flat line, rehooking brought back the noise as did hooking up regular test leads. this only happened on channel B. I sent it back to AESwave who then sent it back to pico for repair and I was informed that different grounds were connected causing a "ground loop" to the unit and current flowed from one negative point to the other and POOF. Not sure what exactly a ground loop was, but given his explanation from AES. I don't ever remember making such connections, not to mention it worked fine on the previous job.
Sorry so wordy, but wanted to be as descriptive as possible and I contacted Pico with this and haven't heard back in over a week and I don't want to risk damaging my Pico as I stated before, I don't recall doing anything wrong in the way of connections that would have caused the first failure.
Just wanted to know is it a cable quality issue or the length of the connection, etc.?