:furious: I'm having this EXACT same problem at the moment with my '96 Ti (Australian name for LE). I got 3.3 V6. I've only had car for 2 months so don't know how long this has been happening before I got it.
Sorry I don't have an answer but I do have some observations which might narrow things down a bit...
1) Mine 'rattle' is (irritatingly) audible from 1300-1500 (ish) RPM in all gears. Less noticable in Park or Neutral.
2) I originally thought it was heat shielding but me and my mechanic friend stripped or tightened the shields with no difference.
3) Fuel's not the issue. I have dual-fuel. A 65-litre tank for Premium AND a 65-litre tank for Liquified Petroleum Gas (LPG). The noise is there whichever one I'm running on at the time.
4) Not detonation. Timing on a dual-fuel car's always tricky but mine's just been done. Besides, I know what detonation feels/sounds like.
5) Because it happens at rev range where gear shift often happens, I'm getting spooked that it may be related to my tranny or T-C, but it's only noise. It 'feels' sweet. I'm 90% sure it's in the exhaust.
6) I even thought it may be the honeycomb inside the cats, broken and rattling at the right harmonic freq (1300-1500 RPM) but the cats were checked and are fine.
I'm tempted to go new exhaust (headers etc) but it's a big investment and I'd like to know before I spend if it will fix the problem. I hope my information is helpful and if anyone gets a good result, please post it.
:sniff: