Recently got a '99 GS300...don't know the history but appears well-maintained, serviced, etc. However, it has a knock that appears to be coming from the engine. Doesn't do it 100% of the time, but fairly often. I'm attaching a link to a video where you can hear the noise at 0:31 and again at 1:00.

Also, may be unrelating issues but also popping codes P0420 and P0440 for Catalyst Efficiency Below Threshold and Evaporative Emission System respectively.

Any help is appreciated.

 

I had a knock very similar to that on my car. The flange that holds the box that contains the air filter was broken. Occasionally, it would vibrate and hit the vendor well. If it's not that, it sounds like something else is loose and occasionally hitting something.

 

Well if you find out you need cats there's a guy on here that has em' for sale..good luck.

 

That is not the engine . It is something loose around there ... no big deal ,. just touch everything and see what is loose , some cover, plastic flap , anything .

 

Maybe a bad PS pump or the AC compressor. Sounds like it knocks when there is load from some kind of accessory. The engine sounds fine.

 

definitely sounds plastic. i put on the headphones to listen. maybe that airbox is flange is the problem.

get your hands in there and get dirty