Audio Systems: car audio problem, input circuits, car subwoofer

Question
i had an audio system installed in my car (subwoofer plus amp) at first the car people said everything is fine but when i turn the key on the sub's make a pop and same happens but 3 times when i turn the key off, when the car is running i can here engine noises from the amp or subs its coming from the back im not sure whats going on.

Answer
The sub amp is wired to the ignition for turn on instead of the ON switch of the head unit.  

The bloop sound or thump with turn on is quite normal if the amp does not have slow turn-on feature OR if you are switching on the main 12 v all the time.  (Power amps have two 12v lines; one is for POWER and is always ON. The other is for switching or activating the amp and comes from the head unit to fire the amp up when power is ready to go).

So, check the 12v wiring carefully; it may be you are not switching the two 12v lines properly.

The engine noise coming from the sub system is another matter all together.  It is car ignition noise getting into the amp.  This can be caused by improperly placed amp grounds or from radio frequency pickup of the ignition.  It must be diagnosed by someone who can identify the source and apply the correct grounding and/or filters to the power lines and input circuits.  It will sometimes be a difficult job.

Wishing you the best,
C