Background noise change after GPIB connection to Keithley 6485

[france2017]

Using the Keithley 488B GPIB to USB to connect the Keithley 6485 picoammeter to the computer. Using this setup we are able to take the measurement from the picoammeter however when connected through the GPIB, the picoammeter detects higher background noise (nA). This means we are unable to detect lower currents (pA) when connected to the Labview software. Without the GPIB connection the background noise level is around 2 pA, is there a method to fix this problem?

Thanks

[RTSLVU]

Sounds like you have a "ground loop" in your system.