The only condition for free use is a credit line. Personal YouTube videos and streams are free even if monetized (promoting a company or paid client work needs a license).
A heavy heartbeat sound effect. Trim it and vary the pitch and playback interval to express different stages of tension.
For urgency, raise the pitch and shorten the interval between beats. For a calmer, more composed moment, or the early build-up to tension, the standard approach is a lower pitch with a wider interval.
