Popping noise in the fuel tank?

why does my car hyundai coupe 2002 make popping/spit noise from the underneath the car. I have been underneath and first thought it was the exhaust but isnt ive been having probelms with ecu light on code p1166 ive changed both lambdas, ht leads, oil filter, oil change, spark plugs, air filter ect i havent done the fuel filter as its in the fuel pump. I yesterday took it for mot and it ped no probelms but this ecu light and popping/spiting under car is getting on my nerves now its just sounds like fuel in exhaust pipe making little explosion as if it was running a little rich but mot man said it was fine.