Odd "rubber band" noise when first accelerating

[ponic]

Hello,

Have a 2004 9-5 Arc. I've recently noticed a weird noise when first accelerating after starting my car. The best I can describe it as is sort of a rubber band noise; where you stretch out the rubber band and pull on it until it snaps back into place. Sort of that rubbery boing sound. It's just a weird sound. It only seems to happen on the first acceleration after starting the car. Does anyone have any idea what I'm talking about? The sound is difficult to describe, but I can almost "feel" in the pedal when it happens.

Thanks!

[rpiereck]

Is auto or stick? Any way you can make a video? That seems very strange.

[Brad Lauzze]

I have felt this in the automatics, both of our 2004 Aeros do it, just like you say, first thing in the morning only, but usually if I'm accelerating and hit a bump just right. Feels to me like something with one of the axle shafts, but I've never really taken the time to look into it. It sounds exactly like is describing it, a rubber band twanging sound.

[rpiereck]

Brad, is your 9-5 Aero automatic too?

[Brad Lauzze]

Yep, all of my cars are.

[ponic]

Sorry for the delayed response! It's been a hectic work week!

Anyway, the transmission is an automatic. I really am not sure how else to describe the sound. It lasts for all of maybe 1 or 2 seconds, then it seems to be fine from there. A little reassuring to hear I'm not the only one with the twang, but I still wish I could figure out what it is! It doesn't seem to happen every single time, as evident by this morning, but more often than not, it's there at the first acceleration of each startup.

Edit: I will attempt to make a video or audio clip of it, but it's a pretty low pitched/not very loud to begin with, sound.

Edit 2: As I think about it, is there anything that may make this sound if the car is not warmed up all the way? I'm pretty mindful of letting the car run for at least 5 minutes before taking off, but some days may be shorter than others.