http://harv.f0e.net/acura/noise.MOV

So my car started making the knocking noise. I lifted it up and crawled under it and the sound is coming from behind the engine/trans/steeringrack and looks to maybe be coming from the cat converter. I verified that the heat shields are secure and the pipe is not contacting anything anywhere.

Is it possible for cat internals to come apart and cause a rattling?

It doesn't start until the car is about 1/2 way to operating temp and is quite noticeable at idle but seems to quiet down as I roll down the road(could be road/wind noise is masking it).

Any ideas?

 

sounds more like an engine sound to me (lifters,rocker ???)but since u said it comes frm the underneath
Did u try to see if the sound increases with Revs ?

why not try to cut out the cat and see if that solves it. U can always weld it back in.

 

It seems to quiet down if I rev up. Now it's having a hard time coming back to idle when I come to a stop. Sometimes it stalls out sometimes it just sinks really low in the Rpms. Once it evens out it idles buttery smooth and there is nothing noticeable while driving.

What is involved in a 135-136,000mile maint?

 

So tonight on the way to workit made it through the 15 min drive just fine with several stops. Still got the knocking. Wonder if this is a time bomb waiting to blow.

 

clean your idle control vavle to fix the idle issues

if your engine is knocking, might want to get it diagnosed and fix it asap. Knocking usually indicates main bearing failure.....

eventually the bearing will seize and the engine will lock up hard, then you are done. did anything happen to this engine to cause this? like over rev, ran low on oil, etc?

 

Nothing rough has happened to this car in the last 36,000 miles. From under the car it seems like its coming from the cat converter. I can't find any exhaust leaks and the pipe is not hitting anything.

 

Exhaust leaks never make a knocking noise and if the exhaust is banging on something it would be reproducable 100% of the time. exhaust leaks will result in a popping or tish-tish-tish type of sound depending upon size and location of leak

Broken motor mounts will show by excessive vibration at itdle, harsh reverse gear engagement, and possible snapping when transmission shifts under high load.

main bearing failure will result in a hard nocking noise at idle that (for a while) will go away when engine is under somewhat of a load and if you go up high enough in the RPM range get really noisy..... changing to a thicker motor oil may mask the sound somewhat but in the end it will still fail...