My suggestion is that you keep the BassImpact at the 4th or 5th notch, that way for most games the rumble will be subtle enough to notice yet doesn't irritate you or effect the sound quality.
Understand that BassImpact is NOT the amount of actual low frequency levels you get.

The Pulse has more range on the mids than on the low frequency, that's why for a closed headset the bass you actually get is quite laid back and neutral.
In other words, you are probably more used to bassy headsets/headphones or sound setups than a more neutral listening experience.

It's normal that it rumbles at almost any sound.

It works like this, the motors in the headset activates and rumbles whenever a certain level of volume hits the 60hz and 125hz band. What this means is that because of how majority of games and movies always has an emphasis on bass regardless of what's happening on screen, the 60hz and 125hz frequencies are always being hit with volume.

Theoretically, footsteps in games activates the ~80hz range but because how plenty of FPS and TPS games meshes footsteps to the environment, it sounds like the 60hz freq is being hit instead.

The motors then rumbles to seemingly "pulse" around your ears.
You ears are possibly very sensitive to picking out low frequencies, that's why you hear the motors even only at the 4th notch.