Elizabethann--I would be very interested in anything you might find out about this subject. I've never even considered that his howling might be for some other reason than the sirens hurting his ears. It never occured to me that there might be some other reason he does it, so I've always just felt sorry for him when it happens.
I don't even know for sure where I got this idea. It's just something I've always associated with pain, I guess! Let me know if you find anything out!