Loud engine sound at start-up

My car did this today after a foggy night near freezing and a couple days without driving. How can I make it stop? Leave the engine running? Wait for dry weather? I live in the Seattle area and it has never done this before.

 

Not sure what happened to my previous reply--I was asking how to make it stop. Do I leave the engine running? Try another day? I live in the Seattle area and this is the first time with this noise, although I have had the "won't start for no reason" a few times.

 

have you looked underneath to see if you still have a catalytic converter?

 

wouldn't it pop a whole crap-ton of codes if that were missing?

 

good question, probably

 

Not necessarily. Often the thieves end up cutting some oxygen sensor wiring which may give you a code (if it doesn't do worse, like blow a fuse and disable the car).

If that didn't happen, the car probably will eventually set P0420 if you keep driving it long enough for the self-test monitor to run.

Generally people notice the noise from no converter before that.

 

Sally, try this to help stop or minimize the knocking.
Fill your tank with high fuel octane from the pump, like 93 gas.
In that same tank use a fuel injection cleaner like Techron. Use recommended amount per fill up.
Do this for two tanks and see if it helps.

This helped me in this cold spell in NJ right now.
I've never had the EGR or manifold cleaned yet with 205k highway miles. I did check and clean the silver metal EGR pipe because it was just 4 bolts every 100k.

it's a quick try and it might help before you get into more involved work.
my2cents.

 

How many miles on it?

 

What other "few other parts" do you mean, by chance? I knew about the redesigned manifold already.