This winter I noticed my wife's xB would make a lot of engine noise at relatively low RPM under acceleration, especially when it first started up. The noise sounds almost like a rattle.

I just noticed that it's now making the noise regardless of if the engine has been running a while, especially with the a/c on.

Specifically, around 2-3000 RPM, under mild acceleration, the vehicle will make a rattly, almost sputtering noise. But in neutral it sounds just fine, and it doesn't appear to be affecting performance any.

I need to take it in, but wanted your thoughts if you have any. I'm a worrywart.

Gosh!
That sounds like the strange exhaust rattle I get between 1,500 - 1,800 rpm.

:tap:

Same with me... Ive tighened about everything i see there is to tighten but it still rattles. Sometimes for me it goes away on longer drives. The dealership not surprisingly couldnt find the problem

Have you tried holding your hood down? I saw a different post a while back, someone with an xB, even made a youtube to show it, He couldn't figure out what the rattle was, then one day (forgot how), he discovered if he held his hand on the top of his rood the rattle went away. Don't know if it's your problem or not, could be since having the AC on with your RPMs up would cause a loose hood to rattle. If you could you might want to try having someone rev it for you and press down on the top right corner of the hood (right in front of the steering wheel), That's where it was on the other guys.