yeah, it's definitely certain sounds that trigger my stutter. i'm German, so the sounds probably are a little different. words that begin with a vowel are generally a problem, those are also the words you englishmen experience as the harshest :D. when i first started working in a firm my stuttering, that had been nearly gone in the last years of school, really worsened. so i had speech therapy for the first time in 10+ years and it really REALLY helped. for the fist time really understanding what stuttering really is, what the core problem and what only techniques to avoid the oncoming stutter was an eye-opeing experience.