Where the hell is that. Noise coming from

The thing that troubles me the most is the "marble bouncing around" sound. Did you identify where that noise is coming from? I think that is very important because you could have something broken. Find where that is coming from FIRST!



AFTER you have located "marble" sound then I would look into the constant growling.



As for the "growling" you are hearing is the air injection valves. There are solenoids (located on the bottom rear corners of the intake runners) which opens the diaphragms and the one way exhaust recirculation valves (located just above the headers) which let's exhaust go back into the intake. It is a function of the emissions system to help get the engine up to operating temperature faster, and to help heat the catalytic converters up faster. The growling you hear usually comes from the air intakes in the quarter windows.

You could have a stuck solenoid that is keeping the diaphragm open? Or a broken check valve? Or a broken diaphragm? You will have to check to see if it is just one side stuck open, or both. The way I would check would be to remove the tubes on the bottom from corners of the air filter box (they lead to the check valve) start the engine and listen to which tube is still making the noise.

 

I just got my car so my experience is very very little. But, my car had some rattles when idling....loose exhaust heat shields on the exhaust, and the ones protecting the engine bay. A little spot weld or two and some washers fixed most of them. My air pump was making a terrible noise, and I removed it and cleaned it, and it seems much happier now.

At first I thought it was a Cat that had broken down, so I was happy to find the loose heat shields.

 

I recall a thread where rivets seem to dislodge themselves from somewhere near the clutch housing? I was trying to diagnose a "tick tickety tick-tick" sound from the rear lower part of the engine. I bought a mechanics stethoscope....cheap and easy to find at any pep boys. Good luck.

 

Hmmmmm?

It is possible you could have a catalytic converter than has burned up the ceramic matrix inside it. That could explain the rattling you were hearing, and the louder exhaust note. The rattling could be broken up matrix bouncing around inside the cat shell or the muffler. You will need to remove the cats and have a look inside to see if they are still good or not.

 

It is normal when starting up. Last longer when engine is standing cold, less when eng is warm. I am told it has to do with emission equipment to allow cold air into exhaust outlet for better burning of a rich starting mixture.
Not a very good explaination from me but what research I did, this was the explanation. I find it embarrassing at first and very loud when listening at air intakes behind the doors. I let the warm-up continue until it stops and gains normal idle sounds. It's ok.