I'll come out and say it. I think the 24-70 2.8 USM II has a faulty design and/or manufacturing issue affecting a multitude of lenses that Canon is refusing to fix under warranty, hoping they can sweep under the carpet. Likely whatever is causing the problem it is not cheap to fix, hence the reason it "does not exist."
REASON: You are not the only one with issues zooming this lens. Other people report clicking noises when zooming, creaking noises, etc:
They send their lens to Canon and often get the same baloney, that noise like that is normal. This is unacceptable especially since its frequently attached to cameras shooting video. Unless you shoot horror movies, I would think lens squeaking is undesirable.
I would call Canon once more and advise if they refuse to honor warranty you will file BBB action, see what your credit card company can do, file a report with the FTC that Canon is falsely advertising a warranty and not honoring it, etc:
CONSUMER PROTECTION RESOURCES:
You may also want to contact this guy, as he had similar problems with a defect that Canon said was normal:
Others reading this thread, all the more reason to pass on this lens and wait for the inevitable 24-70 f/2.8 IS which hopefully will have this manufacturing/design issue fixed...
Ha, IS would be nice! Maybe this is the universes way of telling us all that primes are better. Thank you for the wealth of information, at least I'm not the only one. I will write Canon Service back today and see what there response is. I'm just still surprised that something like this would be considered normal. I will keep you posted and I'll keep the WD-40 at arms length in the meantime