Having taken my car back to Vaux three times for a front end knocking noise-

1st time- They said nothing was wrong
2nd time they replaced a tyre arm on one side despite it being noise on both sides.
3rd time, today, they say the spring insulators are worn and there is a load of debris in there causing the noise....

I have no idea if this is right??? Also if they are not under my warranty its going to cost me £140 odd, is this easy to do yourself?

Any advice appreciated!!