Mine is much louder, although I did notice that if I put a finger over the speaker it pretty much kills 99% of the volume. This wasn't the case on the earlier models, so I assume it's from the denser manufacturing, and the stainless steel edging. I mention this because I think that might be the case with your bumper.
Could you test it by taking it off? I'm interested in the Apple Bumper but would like to know if I'm going to sacrifice audio. Thanks.