The "bump" is indeed the antenna for the XM radio. New addition for the 2004 Accord, at least on the EX, I guess just on the EX-L and EX-V6 if you said the std. EX doesn't have it. It's not really that big, is it? Don't know how easily it could come off.

I know a few people that said they were not interested in XM, they tried it out and said they will never go back! I think you get like 3 months free trial when you purchase a new car with one, of course this is to "hook" you to it, but I know you do have to call and "activate" it when you buy a car w/ it.