Two things I guess. First, are you not for a reason? Does it not sit comfortably with you, are you embarrassed perhaps? Or something else? We Kiai often. In Kihon we kiai every time we turn for example. In Kata as you say there are various points to kiai and in kumite we are expected to kiai (one step or five step we do and in sparring you're more likely to score a point if you kiai) you likely know, but doing a kiai, the act of it itself is a release. Its a shout and importantly doing so will make you tense your stomach. An example is if you are doing one step and you attack your opponent and kiai, he blocks and counters, with a tensed stomach you can take his counter (if aimed there). I use the kiai to increase the intensity of my move. Controlled aggression you might call it. If you see it as this, you can learn to use the kiai to your benefit. If it is just that you are not comfortable doing it, just realise that everyone is doing it and no one really pays any attention to the kiai someone makes. Just remember, dont actually shout the word "kiai". I myself (I think!) sound more like "die" though thats not what Im saying, its just a yell.