I'm confused... have you identified that a specific note from a bass guitar , keyboard, kick drum, etc. is affecting the video from the projector? If so why can this not be handled with basic EQ from the mixing console or PA processing?
If on the other hand you have some unknown interference with the projector and you are asking for troubleshooting steps (cable, lamp ballast, etc.) I don't understand why you say it is a bass note causing the issue.
Can you try explaining a different way and perhaps be more specific on how the DLP projector is being affected?