Speaker Grills??

I put on my speaker grills on my Hales T5's to see how it would look and sound and it looked OK and sounded OK but the difference in sound with the grills off is actually significantly better than with them on. With the grills on the sound was restricted and kind of muffled. With the grills off the music opened up and had much more life to it. Is this normal? The difference with the grill on or off is not subtle. I cannot listen to my Hales with the grill on as the difference in sound is so different for the better with the grills off.Is this normal?