trouble making tremolo smooth

Hi David!

Thanks a lot for all the great material you are providing, your site is of great help in my harmonica studies :) however, after playing most days a little for a few months, my tremolo still sounds terrible. I am able to do tremolo on blow and draw and with different tempo, but it sounds rather mecanic, not like a sine wave but rather like the air is coming out of the harmonica in regular puffs. I don't now if you get what I mean here, but I'd love some advice/exercises to help improving the technique!

Best,Ellen