You don’t need a Hollywood budget to get great audio. There are many libraries where you can download royalty-free suspense effects: Building Suspense in Filmmaking: Techniques and Tips
It’s not just about the sound itself; it’s about when you use it.
A rhythmic thumping that mimics a person's pulse. It’s a psychological trick that makes the listener's own heart rate speed up. 2. How to Build Tension Like a Pro