I've had this same problem on the e and b string. I keep my action really low and therefore it's more subseptible to the "twang" as you call it. You mentioned putting in a new saddle. Have you checked the neck properly? Contrary to popular belief a neck shouldn't be dead straight. Most styles favor a slight up bow in the neck. A neck that is too straight will cause this problem. The problem will also develop sometimes when you go to a lower gauge string and can be corrected by going back to higher gauge strings. If the neck is right and you still have this trouble and your action is equal to or higher than 4/64ths at the 12th you may need to just get the frets leveled and buffed. That is if they're not dug out too bad. If they're too bad and you have to replace those frets it shouldn't be a problem or big expence. A good reputable luthier should replace the frets in question for about $15-20 per fret. Hope some of that was helpfull...Peace!
[b][color=#FF0000]If your brain is part of the process, you're missing it. You should play like a drowning man, struggling to reach shore. If you can trap that feeling, then you have something.
[/color][/b] [b]Peace of mind. That's my piece of mind...[/b]