dont really know what this is so im posting in general tech. have a 2005 a4 3.0 6 speed with just over 100k. when i was driving today i heard a weird rattle noise that i couldnt pinpoint where it was coming from(i said it was coming from the front and my friend said it sounded like under the car). it occurred in first gear at just over 3000 rpms and very slightly in 2nd under the same load. i pulled over to see if the noise still happened when i was in nuetral but nothing. anyone have this problem before or an idea what it could be. is my first gear on its way out? also no difference in drivability that i can notice. any help is very much appreciated

 

Could be a loose heat shield under the car. There are several that provide heat protect from the exhaust. Sometimes they might loosen up a little and cause a rattle.

 

thanks for the reply. That was my initial thought too but it doesnt sound like any heat shield rattle ive heard before and it is only when im in gear. I cant get the same sound in neutral no matter how high I rev it. Also I banged around a little bit under there and it seems tight. Anything else it could be?

 

Check the transmission and motor mounts. If one of those is shot, it could be causing some metal to metal coming together under a load (acceleration, deceleration). If it's in neutral, there is not a lot of flex in the drivetrain to cause loading.