Sound and when accelerating from a stop

Good night all, Ive been having this issue with the truck, sometimes when I accelerate I hear a sound from the engine bay, when this happens it usually feels like the truck accelerates slower, so i have to push the pedal a lil bit further in order to get better acceleration, seems like it comes from the exhaust but Im not sure, this has been happening for more than a year, dealership couldn't reproduce the problem, and apparently they know rats about the trucks . I recentrly switched from 87 to 91 octane gas and it doesn't helped at all.

any thoughts?

 

Ok ill try to record a video tomorrow, but what about the accelerator not responding?

 

Yes sir, and then I push the pedal a lil bit more then the sound comes and then truck accelerates, just like some kind of delay if that makes any sense