I have a 97 f150 4.6, when I'm towing a load and trying to accelerate a little harder either to just gain speed or climb an incline I get this terrible crackling noise from my engine as if I was low on coolant or low on oil. But all my fluids are good. It even does it when I'm climbing an incline not loaded. Any ideas what this could be?

 

Detonation?

 

Huh? I'm sorry I don't understand!