Noticed the rattling/ticking sound recently at idle when engine reaches to running temperature, cold engine start doesn't have this sound. AC on or off doesn't change the noise. Clutch is bad to be replaced, but the noise doesn't sound like clutch chatter, and press the clutch doesn't change the noise. Vacuum gauge reads 21 psi which is good, oil level is at the right position. Anyone know what might be the problem?

 

Rod knock. Coming soon - big hole in the side of the engine block.

 

I think the noise goes away when rev up the engine, I will check this week, im assuming the noise should be pretty loud underneath the car if is rod knock?

 

There's really no way I (or anyone) can properly diagnose the problem just from the sound on your video. A rod knock i my best guess, though. You really should have a good mechanic have a look before you do more damage. Maybe you'll get lucky and it's just a pulley or something external.

 

it prob doesnt go away, it is just faster so you dont notice it as much

 

made another video after work, cold start it sounds normal, no rattling noise in the first video.

 

Cold oil is thicker and may compensate for loose bearing clearances. Oil pressure will also be higher, but all that matters is how the noise is at operating temp, because that's how you drive it. I still say rod knock, and this new info still fits.

 

I drove 10 mins after water temp reached to 87C, no noise. turned AC on and drove around 5 mins, the noise came on, not as loud as the sound in my 1st video. I am going to do 3 things to check if is rod knock
- drive a little longer without turning AC on
- after rattling sound comes up, disconnect the spark plug
- change flywheel and clutch (need to do it anyway)
- if noise still there, go to dealer.

 

checked out some bad cat rattling videos, it really sounds like a bad cat. will check cat 1st

 

maybe a bad engine mount?

 

Update: Replaced the clutch/flywheel, and changed to test pipe. the rattling sound is gone. the clutch is completely worn.

 

Glad to see you found the problem.

 

I got the same noise on my z. Just got resonated test pipes hoping the sound was from that. I'm guessing its the clutch then, got a JWT clutch with only 7k miles. Will check it out.