Sorry this is so long. I reasently had strance low rpm revs when im stop and in park followed by a knock from my engine. the knock carrys up till around 10 mph then stops, another thing i noticed is it only does it when its hot out. i have also found that it does not do this when the a/c is off. norrmally this would not be and issue for me because i could roll down the window and be fine, but i live in arizona. please help i need to get this fixed and would love to have it figured out better before taking it to the dealership. thanks and again sorry for the essay.

 

Simplest thing might be a dirty mass air flow sensor.

Do you have an aftermarket filter or intake on the car? And check engine lights?

 

I have an after market intake no check engine lights but this has been happening before the intake.

 

How's the freon pressure?

 

Is it happening while you're sitting still? No noisewhile idling but when you turn the ac on it sounds like a constant noise?

 

My car used to do that knocking sound too!! I just let it ride out and then one day it was gone lol!

 

ok so its the freon sorry for the long wait on the reply, i plan on fixing the issue today