Today I've realized my 70-300 zoom does not rotate fully. In fact, it stops just before the 300 sign is reached in the ring. There's some metallic noise inside the lens when I move it, which let me guess that a mechanical part is broken inside. If I put the lens in vertical position and then I rotate the ring I can reach the 300 sign. Focus works just fine, except when I try to focus when the zoom is stuck before the 300. In that case, the lens moves back and forth as if something is holding it still. I'm going to bring the lens to the Canon customer service, but I'd like to understand what could be wrong, just to be prepared.
Any thought? Oh, I'm not aware of any physical damage to the lens...
