I have a 1997 Audi A4 turbo that is making a faint knocking noise. What can this be ? And can it be the smog pump is going bad?

. Install colder running spark plugs.

. Use higher octane gas.

. Use full-synthetic engine oil that meets Audi's specifications for your car. This can reduce octane requirements and help the engine run cooler, among other benefits.

If the problem persists, install a slightly lower temperature thermostat.