I'm 1000 miles away from my car this week, so can't today, but yeah good idea. Not sure how I can do that, since it doesn't happen with the car idling. But maybe I can borrow a friend to stand on the road and see if he can pick up the sound on a drive-by...

loose parts inside muffler or Cat?

Nope. Have had both g pipe and cup pipes on , and the cup pipe used a different cat. Also replaced my heat exchangers last year. So each component has been off. Never affected the sound.

+1

I hope not, I'm already replaced two!

This sounds like a good possibility...

+1

But then this thread seems to change (from a faint ringing noise, now the focus is a rattling noise... Funny, I hear both noises coming from my car.

I hear the same rattling noise, seems as though it's coming from the passenger side. I hear it at low speeds and it sounds like it happens after going over a small bump in the road, I thought it was loose bumper hardware shaking (rattling) back and forth after a bump. Everything I've touched seems solid, but I need to get it up on a lift...

No cat, and it sounds like it's coming from the other side.

I only hear the "hollow marble noise" when driving down a bumpy street at low speeds. Not while idling.

+1 frequency of the marbles in the can doesn't change with the rpm.

I don't have a video (yet) of the marbles, but I found a video of the faint singing noise.
I heard it could be coming from the harmonic balancer? (I can see a slight wobble)

Took a little while to capture the sound, it seemed that on the days I had a camera with a decent microphone ready the sound wouldn't be as audible. So here is what I have from three different days. Might have to turn up your volume a little.

Starts being distinctly audible around 15sec mark

Also, excuse the butt to the camera in the beginning, I had just replaced fuel filter and was checking for leaks.

Alex,
I think I can here it in your vid. It's faint though.
Do you hear the same noise in mine above??

It is tough to get a mic to pick it up well, but it is a faint sound for the most part in my case. Loudest at start up. I don't hear it in your video, to me it your sound is more a steady whine than a ringing.

Ah....

Now you guys know you bought air cooled cars right? :thumbsup:

I thought you had a harmonic banging or grinding, sounds normal to me. These things make those noises. Unlike a water cooled motor there is nothing to dampen all the mechanical internals. Just tap on the fan, shroud, cyl cooling fin, even a lwfw all make a particular ringing sound, the fan makes a howl that I've found particular to each car. I know you know all this but my point is these motors just make these noises, it's part of the charm, enjoy the drive:thumbup:

Thanks Alex and J.

Like you said, these cars all make different noises (and each drive differently too). I can hear the ringing, tinny noise... but I guess it's all part of the cacophony of noise coming from back there.

With that settled, I'll start researching more about fuel lines... lol.

To the other noise I was hearing....

I think this is the cause of the rattling noise I hear in town when I go over bumps in the road:

91 C2 Hollow Ringing Sound in Engine Bay
 

I realize these cars make noise. I can't tell Alex if yours is like mine. So next NE9O meet we can have a listen...

My noise, and the noise that has been described, is not "noise these cars make". I've heard plenty that don't make the same sound.

Still hoping it's something easy or benign...so far the motor hasn't fallen out the back...knock on wood...

Mine does it too.

I think it's exhaust related. Something just needs tightening up.

'94 C4

in the clip above does the audible ringing sound go away when you close the door?

Have you checked to ensure the fan isn't contacting the housing at any point?

I do agree that these cars can make a variety of sounds, and smells in some cases, but I don't really the sound being there for the first two years I had the car. But as a new development, if I drive next to a wall or barrier on highway, I can hear a slight raspy tinkering, and in some cases it will increase with RPM. So I'm hoping its something loose, just can't wrap my head around what it could be. All exhaust clamps and mounts are tight.