Yes, this can be normal. With some Canon lenses that have image stabilization, Live View keeps the IS system active continuously, similar to holding the shutter button half-pressed. That can produce a faint ongoing hum or whirring sound from the lens. Since you confirmed the noise only happens with the EF-S 55-250mm IS and not with another lens or with no lens attached, the lens’s IS is the likely cause rather than the camera body. If the sound is very quiet and the lens otherwise works normally, that points to normal operation. If the noise becomes unusually loud, changes suddenly, or the lens shows focusing or stabilization problems, then having it checked by a Canon-aware repair shop would be sensible.