Vibration noise in '99

[Bruce J]

In my '99 Cruiser I've had a high frequency harmonic vibration noise coming from the engine area. It sounds like two thin metal plates vibrating against each other. It's worse when I first start it up and accelerate lightly. It doesn't occur under no load (unless on first start up) or under a steady load. It is not related to engine speed. And,since it typically only occurs while underway, I can't get a look at it while it's happening.
A friend had told me that it was the heat shield plates over the catalytic converter, but it's definitely not coming from that area (the sound is much more forward, in the engine, even front of engine area). Any other ideas?

 

[Koffer]

Check for any heat sheilds that are on or around the manifolds. Also check for any that maybe loose on the firewall. a rubber mallet will help by hitting the ex system, frame rails etc .
The part thats making the noise may not be "hanging" off but may have stress cracks at the mounting points.

 

[Bruce J]

Thanks, Koffer. I tried the mallet test and think the noise might be coming from the catalytic converter heat shields after all. There's definitely a similar sounding noise coming from there when I tap the exhaust pipe behind the cat. I pulled the shield apart a little where they were vibrating and that seemed to make some difference on the mallet test. Is there a way to fix the problem completely, like some sort of heat-resistant gasket that could be inserted between the shields?

 

[RHINO]

maybe some fiberglass insulation to stuff in there?? this is the problem with modern rigs, too much stuff to vibrate.