Why does my Audi A4 engine make a strange knocking noise?

I recently purchased a used Audi A4 and have noticed a strange knocking noise coming from the engine. It doesn't happen all the time, but it is concerning. I want to make sure nothing serious is going on.

It sounds like you may be experiencing engine knock. This is a common issue in Audi A4 models. It could be caused by a few different things, such as low-quality fuel or a faulty spark plug. I recommend taking your car to a trusted mechanic for a proper diagnosis and repair.

I had the same issue with my Audi A4 and it turned out to be a faulty ignition coil. I would suggest getting that checked and replaced if necessary. It's a relatively easy and inexpensive fix, but it can cause serious damage if left unaddressed.