volcane

I have a L reg TD volcane, it only has 77k on the clock, but recently its started to really shudder /knocking sound coming from the engine in 1st and 2nd gear. BEfore I take to the garage would like to know if anyone had same problem. I really hope its not the gearbox, as that will cost more than the car is worth to get fixed , and I really like this little ZX. Its only in 1st and 2nd gear the rest of the time it is fine.