Hmmm, does it feel like all sounds are muffled, or just those at the extreme right and left sides? Try inserting the tips with the faceplates rotated forward (counterclockwise on the left side for someone looking at it to your side, and clockwise on the right). If the tips are wide, then you should just need a very slight rotation back the other way to get them to lock. You can rely on the tip's width for the seal, rather than a full rotation, since a full rotation IME can cause the muffled/congested sound you may be experiencing. If that doesn't work, then don't be afraid to ask for an adjustment, and be specific about the problem and the fix you think would work. In all likelihood, they'll probably just reduce some of the width that they just added.