#1
So, I've just gotten my new Ibanez SR305, and I think there might be some trouble with the B-string, since it's set so low that all I get when I play it is an indecipherable rattle that annoys me to no end.
Is this normal?
#2
Are all the other strings OK?

If so, check the nut. If that string's slot is cut deeper than the rest, that may be your problem. Alternatively, it may be that the bridge isn't set up right so have a look there as well.

If it's a brand new guitar which isn't functioning correctly though, you should take itback to the shop as any setup work will be covered by warranty.
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#3
Welcome to the world of Ibby SR owners. Great basses, fast necks and tonally wonderful for the price.

However, they seem to need setups more than any other bass I've owned. They are very susceptible to changes in weather, humidity, string gauge changes etc. Your string issue may be any of the issues mentioned above all the way to a full setup. Read the FAQ and if what Ben has written doesn't make sense, then take it to a shop and have them check it out. If possible, ask them if you can watch them do a basic setup (if that's what's required), so you can do it yourself next time.