It is normal as in a known problem that happens to just about every new age car. It's not however normal in the sense you don't need to get it fixed! Subaru really should have done a recall on it to fix the problem, but never did. The problem occurs on most cars while it's still under warranty, so in most cases Subaru will just fix it for free. I assume your car is out of warranty now, but it may be worth asking a Subaru dealer (or two) if they will replace for free or at least for discount as it is a manufacturing fault. If not, then you may want to consider replacing with different suspension, as it will probably be cheaper than OEM items for much better kit!