I am not going to post the problem since I found somebody else a few years back had posted with the exactly same problem and they described it impecably, so here is what they said (BTW they received no reply):
""""My 2000 GXE automatic has had this problem essentially since I bought it: when the car is accelerating and is revving at about 3000 RPM and up, something in the front of the car makes a clicking or rattling noise. It sounds kinda like baseball cards in a kid's bike spokes.
I originally figured I had a branch stuck in the underpinnings dragging along, but no such luck. It happens more frequently when the engine is cool, though I heard it a few times during a road trip a few months back. It used to happen only at about 3100 RPM, but it's started becoming less selective recently--I've noticed the sound below
3k RPM and into the 4-5k range. It is most prominent when I first pull out onto the highway, though I've yet to hear the sound below about 20 MPH.I've taken the car to the dealer twice, and it's refused to make the sound either time. I'm leaving the car overnight on Tuesday to see if maybe it'll show up (The dealer is about 30 miles away, and I figure the engine is too warm to do it frequently after I drive out there). However, the mechanics seem to be totally stumped, so I was hoping someone on this forum could be of some assistance. Thanks,""""
In regards to my own problem I bought this car with 37k on it (54k now) and it's had it as long as I can remember.
Thanks if you have ANY idea what this could be :) My car is a 5 speed and it happens in 3rd, 4th, 5th gears (mostly 3rd when pulling onto the highway in the rev range mentioned).