True story on the knock though. If anyone hears this with their FA20 engine it would be very wise to just pull over, especially if you have any engine or drivetrain mods. Toyota (from experience) will use it to get out of any warranty work that causes the engine to cease, if they can. I ended buying my own replacement FA20 engine because my #4 rod broke and punched a nice "H" shape hole through the short block, while the car was idling in a parking lot I pulled over in.
I paid Subaru to break down the engine block since Toyota (Scion) dropped my case because of aftermarket parts. The Subaru tech wrote a sworn statement and took pictures of the breakdown to illustrate the faulty part...but I ended up not pursuing further action since Toyota won't take a paid and trained Subaru technician's word...even if Subaru designed most of the damn car. LOL.
But love my car now... not even remotely stock
So bottom line... don't mess with the knock lol