I have a 2007 RX350 with 140,000+ miles. The engine is making a rattle/knocking noise. Would like to know if it might be the catalytic converter and what it might cost to fix. Really don't want to take it to the "stealership" and pay more than I should to get it fixed. Any feedback would be greatly appreciated.

 

Try a bottle of chemtool b12 fuel injector cleaner for $3 bucks. Your fuel injectors / combustion chambers are probably dirty if you never cleaned them. And clean your mass air flow sensor with a bottle of electronics cleaner. You will be surprised how well your car will drive just doing these 2 items. And it's cheap maintenance

 

If it's not the cat, failing water pumps can rattle:

https://www.clublexus.com/forums/rx-...inal-went.html