So I just found out how to turn on the Live View mode on my Canon EOS 40D (turns out there's a setting for it, big surprise) and I was pretty surprised to notice that while the camera is in the Live View mode, it produces a continuous noise (not sure if it's coming from the body or the lens, though I suspect it's the lense). It's pretty quiet, I wouldn't have heard it if I wasn't sitting in my room with no other noise around. Sounds a bit like a running computer fan. Is that normal or is it a symptom of some kind of malfunction? In the Viewfinder mode, the camera is completely quiet ...
EDIT: Following @null's advice, I tried out a couple of things. The noise is not present when I take off the lense and activate Live View. I have also tried another lense, which doesn't produce the noise as well. It's only occuring with my Canon EF-S 55-250mm IS lense. Is that normal?