What could the the cause of hearing like someone getting hit in the stomach (possibly vacuum leak?) at the intake manifold when i tap on the gas pedal?

 

Hello,

From your description, it sounds like a normal operation for any car, since abruptly depressing the throttle releases a lot of vacuum all at once, creating that sound, though you will have to post a video of it for any specific conclusion.

Hope this helps and best of luck!