Rattle on rev-down

[seattlejester]

Hi guys, I was hoping to get a couple second opinions on a noise I am trying to track down.

 

240z

7mgte

R154

Custom driveshaft

R200

 

I've just recently checked the rear suspension bolts and added lock tite to the cross member bolts.

 

It's an intermittent rattling noise. I can best get it to occur consistently when the car is warmed up and I rev the engine and let it rev down. It occurs about 1000-1500 rpm from best guess. 

 

This happens when parked or driving. 

 

I've checked to see movement from the driver seat through the transmission tunnel, the driveshaft and exhaust don't seem to be moving so I think it is safe to isolate the noise to the front end.

 

It could be something as simple as a loose fuel line, but I just wanted to see if anyone can offer alternative ideas as to a noise of that nature. 

 

I think I've convinced myself it most likely is not drive train related, but thoughts would be appreciated.

 

I'd best like to tackle the problem head on with multiple possibilities.

Edited April 6, 2015 by seattlejester

[dexter72]

So the noise doesn't happen when the engine is cold or it isn't as consistant when the engine is cold???..

 

You can try using a long screw driver and place it on random parts of the engine when the noise occurs. Place your ear on the handle and where the noise is loudest is where the noise is coming from. I would check the engine first, then engine components, then exhaust, then trans.

 

I will P.M. You with a little update

[seattlejester]

Isn't as apparent when cold, I usually don't pull the car out till warm, but I don't hear it in the same RPM range when cold.

 

I was thinking the old screwdriver trick. I'll give it a shot.

 

My worry was that it was a tell tale sign of a loosening flywheel or something that I'm not particularly experienced with that someone might see and recognize right away. 

 

I'm leaning towards something loose maybe the exhaust or a fuel/brake line, it just is a circus act to try and rev the engine and then search for rattling components. I'll have to recruit a friend, but I thought I could use my virtual ones till then.

Edited April 7, 2015 by seattlejester

[jeeper42]

If it's the flywheel loosening, you will hear a change depending on if the pedal is depresse. Just went through that on mine. Your best bet is to use the screwdriver or a stethoscope to track it down.

Edited April 7, 2015 by jeeper42

[seattlejester]

That's what I figured or maybe binding during start up or something or more noise during initial clutch contact.

 

I'm just going to slow my brain down and go with the stethoscope and find the sound before I jump to conclusions glad to see no one is telling me that it is a definitive indication of something.

[seattlejester]

Took a look at it this weekend. 

 

I was so concerned it was coming from the transmission tunnel, it was a fairly loud rattle. But when I popped the hood the noise was not as apparent. I let the car warm up and took a listen and I think I found the culprit. It was the fuel feed line bouncing off the fuel pressure regulator on the return line. Some witness marks indicated the noise from the scarring on the AN fitting. 

 

Thought is that after the engine warms up a bit the engine mounts become a bit more pliable. And the rocking moves the regulator just close enough to the return line to rattle as the engine settles.

 

Wasn't able to replicate the noise after I secured the line so either it needs a drive to make the mounts even more pliable or the noise is gone for now.