My 2003 Volkswagen Polo has 18,000 miles and over the last 5000 miles has developed a tapping noise from what I thought was the valve gear, as it sounded a bit like a hydraulic tappet - the noise rises/falls in line with engine revs, but is present hot or cold and is of constant "volume" after one minute of engine running or two hours. It wasn't due a service but I tried an engine flush, new oil (5/30 fully synth) and then had the hydraulic tappets changed recently, as the ticking was driving me mad. I couldn't think that it was anything but a dodgy tappet, but the local indy garage did say that they had doubts and thought the sound was a little too metallic to be a tappet.

Anyway, changing tappets didn't work, the noise was still there. The oil pressure is good and then we isolated the injectors, finding that unplugging one of the injectors stopped the noise. Thoughts now are that it could be internal, such as piston or small end. I can't believe that it is a small end and from your report, I see that some Polo's suffered from leaky injectors that caused bore problems, but I don't know what the effect of that is. Any pointers?