So I've been riding my 1981 280zx around and for the most part, it's good. but there is an issue at weird and spontaneous times. I hear crackling going off when I drive. The best way I can explain it is it sounds like small sparks of electricity/leaves crumbling. I thought it was just debris at first but then I noticed it happens at times when I rev my engine. the engine does not overheat, it stays between 120 and the midpoint (190). Nothing is leaking from the car, I had UV in the coolant and there are no leaks. I check my coolant levels and they seem to be consistent. any idea what this could be?