I have several 8594E analyzers failing the Noise Sideband test at 500MHz with 30kHz offsets. The specification is -75dBc. The units are typically measuring around -74.7dBc. I have tried the E8257D-UNX, E4438C-UNJ, 9640A-LPNX, and a host of other generators. Out of about 20 units, at least 8 have failed this test. Has there been any specification changes? I have tested them at different locations and different benches but they still fail. What should I look for next?