No, really.
'97 A4qm 2.8 w/ 91,000 miles,well maintained.
Is there anything that would contribute to engine knocking, other than octane? I run the highest octane available, but still get knocking under acceleration. It's almost embarassing. More noticable in warm weather, but that could be because the windows are open.
Maybe if I turn the radio up.....

if it's sudden then maybe since your last tank of gas?

There's lots of reasons why it could be doing it. I'm just floating the theory that you got bad gas... which has been happening A LOT since the prices have passed $2.

I find that when I don't have enough oil (1 quart low) the lifters start making some noise. Adding some oil takes care of the problem.

Hopefully that will cure your "knocking" noise.

Bob

It's been doing this for a while. I buy from a busy station, so I'm reasonably sure the gas is fresh.

It would be helpful if you could have some sort of shop or local helpful person check the error codes - it saves a lot of effort tracking down problems. The problem could be any number of things; fuel injector, ignition coil, etc.

You might try pulling the spark plugs and wires and looking at them - pay special attention to the spark plugs and see if one or more appear to be in worse shape than the others - if two spark plugs look especially bad one one side of the engine or on opposite sides of the engine that could really narrow it down.