Engine Mechanical problem
2000 BMW 316 Two Wheel Drive Manual 101500 miles

i have a bmw 316i, its just passed its mot and just been serviced. but i still have a problem, when am driving the car it jirks, this happens especialy when i put my foot down on the gas. i think it might be the feul pump, i hope not as i guess this would cost a lot lf money to get fixed! but what else could it be?? please help. thanks, paul.