I can only hear my music and nothing else. - Marble movement is super smooth. Really like this case. My toes touched the end but werent crammed or anything. I have worn Birkenstocks (previously referred to as birkies before the moniker became a spinoff brand) for many years, I have always purchased the originals and mentally prepared myself for the lengthy, painful but necessary break-in period. First off, the size is True to Size. Größe und Gewicht der Flascheentsprechen einer gefüllten Trinkflasche. Sizes can be inconsistent between different countries of manufacture. Only complaint - straps to adjust are flimsy and hard to adjust. I returned them and they did give me a full refund.