75 Engine compartment noise

[75sled]

My 75 suddenly started making a noise. The noise is coming from the lower left rear of the engine/exhaust area. The sound it really hard to describe, but the best thing I can come up with is coins in the clothes dryer (maybe not quite as loud as that). The noise is very eratic (no rythm) and it comes in goes. However, I can't seem to figure out what makes it come and go. I first thought maybe it was the starter bendix being old. So I rebuilt the starter including a new bendix. No change. I haven't done any other work in that area so I am not sure what could have caused it or what it could be. It will do it at an idle in park or in drive it will do it under exceleration or coasting.

["75" Coupe]

Man I have looked around my "75" for anywhere that could make that noise and am left without any clues ?

I would get your digital camera and take a little video of the area and the noise, upload it to YouTube and maybe someone here could identify it ?
Just a thought...

[75sled]

I will see what I can come up with from my cell phone. Not sure if my digi camera takes video. I will have to look at that as well. Good idea though. I'll give it a shot.

[jayoldschool]

Exhaust crossover broken and flapping around? Check the bottom of the manifold where it goes into the pipe. Although, I'm not sure if it is on that side, or if that car even has one...

[75sled]

Is that the little vacuum operated door inside the manifold?

[jayoldschool]

That's it! It would look something like this:

[75sled]

I did look at that. I am assuming from the looks of it you just remove it from the manifold and replace it. What exactly is its function?

[jayoldschool]

You don't remove the manifold, you remove the down pipe attached to the manifold, then that piece.

When the engine is cold, it closes, and forces the exhaust through the crossover to the other side to rapidly warm the engine to operating temperature.