For some little copper washers.

At first we thought it was the exhaust manifold making a blowing tappety noise, so got that fixed, started it up and it was still making the noise.

On closer inspection it was one of the injectors blowing past the copper washer. So out comes the injector to find there wasn't even one in there.

We must have forgotten to put one back in when we did the head gasket.

She sounds awesome now and much faster too. Although that could be psychological.