I had an ongoing thread about my cats but it sounds like its coming from under the hood now.

So at around 3K rpm my engine (I think its the engine) is making a vibration/knock sound. Its consistant, if I rev constant between 2800 and 3000 rpm it makes the noise.

2003 OBS now at 39K miles. I get scheduled maintenance and oil changes without missing so far.

I use Suburu oil filters but I'm wondering if the mechanic I brought my car to, accidentally put in the wrong oil. 5W-30 is as common and he could have put in 10W-30 or something.

Can any engine Gurus agree or disagree with this theory being a possibility?

Anything else I can check?

Thanks,
Chris