I have the same problem.
Somewhere around 1200-1300 rpm there is harmonic low pitch growling like sound that seems to come from the front - best guess is low to the ground in the center of vehicle under the hood maybe a little closer to the passenger side (feels like it's coming from just in front of the center console towards front of vehicle).
No grumbling is detectable when not in gear and car is revved to culprit RPM value (neither neutral or park) so it seems car must be in gear -- also, speed seems to play a role as 1200 rpms at some speeds it is not present (or at least not as pronounced) it is wost around 38 miles per hour and you get in the sweet spot of 1200-1300 rpms. Same speed at another rpm there is no noise.
I think I can hear it through all gears at that rpm but it may be my imagination but it may be there at a lower volume that I just can't hear it over the road and wind noise.
Took to dealer and thought it was alternator and it was replaced -- no effect.
40,000 miles, SXT.
Thanks for any input.
Rodney rpg007@aol. Com
Monday, June 11th, 2007 AT 11:04 AM