This is an excellent forum.
My 2001 Montero Sport started making a slightrattle noise at 45,000 miles. You could hear it while sitting inside the car. The noise came from the engine area, lower part of the firewall, passenger side. I brought that up to the Mitsubishi service manager everytime I brought the car in for service, but he was either deaf or pretended that he couldn't hear it. I have now moved to another area, and at 110,000 miles the noise is really noticeable, especially when stopped at a red light. Whatever it is that is making the noise needs some tightening, but it is nearly impossible to hear it and pinpoint it with the engine running. However, when back inside the car the noise is there. Has this happened to any of you, and did you fix it?
Thanks.

 

Maybe a loose skid plate or exhaust part?

I'm no expert but I'd try to pinpoint it while in the car. Maybe use a mechanic's stethescope to help with that.

Once you've gotten the best area where it might be I'd pop the hood or get underneath and continue looking using your ear w/ & w/out the stethescope.

 

It sounds like it could come from lose exhaust parts.

Use a stesthoscope? I didn't know they made such a tool.
Searched online and there are many options. Thanks, I will do as you
suggest. Will post back as soon as I find the source of the noise....