Ladd i work with recently bought an Astra 1.416V (Vreg) it's only done 15K but it's been tapping/knocking scince he bought it

It's under warrenty at the garage and he's had it back to them - but before he took it back he took it too his local mechanic for his opinion - he said it might be the Hydro Lifters??

anyway the garage he bought it off has had the car 10 days and it's been to 3 differnet garages as no one wants to deal with it, he's just recieved a call to say that it's the Tappets?!

Are the warranty people trying to get out of changing these HydroLifters?

What are Hydro Lifters? Expensive?

Any help appreciated as the more Ammo the lads got when comfronting them the better