You can change the sensitivity of the haptic feedback in settings. I myself just set it to full and tapped the back and nothing happened, So it may be possible that your device may be faulty, but then again, it could just be that it is super sensitive.
// Nexus 5 (D821) // Liquid // UBER //
Note 3 (SM-N9005) // AOSP ROM of variety // Lean or temasek's Kernel // - Dumped. No more Samsung