If your sx100 has old type of electronics (visualisation board), the composition (adding texts, lines, applying LUTS, overlaying a scalebar) of video is done on visualisation board, which have its own memory, and old memory can get corrupted. I .e. our old visualisation board has faulty LUT memory, and random bits flips adding colors randomly (off course that is not seen in acquired and saved image), reloading luts fix issue (temporary).
In your case it can be faulty memory of overlay layer (texts, markers...) or memory for temporary storage of signal (as 8bit gray data). Anyway that is not VME bus issue, as else you would see the same patterns on acquired image to PC (which bypass, or more precisely - that process does not include visualisation board at all). With new gen powercquicc II processor (which replaces old Motorola 68030) and new electronics (actually scanning, visualisation and acquisition in the single pack) the RGB composition is done (I am near certain, but not 100% sure) in PowerQuicc II processor, and same image is sent to PC and physical monitor (tailored with additional elements overlayed).
We have such configuration on SXFive, and we are getting vertical stripes on all images (phys. monitor and PC) - I cant find where that noise is coming from, and this actually could be bus related, indeed.