I suspect this is not going to end well, but I thought I would seek input. Have a 2004 Dodge Stratus 6cyl auto daily driver with 164k miles. It gets the job done and has been remarkably trouble free. I'm not sure if the auto trans has ever had fluid changed, although I suspect not.
Starting a month or so ago, on cold start ups, usually when outside temp is in 30s or below, shift into reverse or drive with the brake on, and car still, there is a pretty raspy sound from what seems like the transmission. Think sand and pebbles in a blender. No significant vibration. Once I touch the gas and car starts moving, it goes away. Once the car is warmed up, the sound goes away. It shifts fine, as it always has. My first thought is change the trans fluid. I think I read somewhere that you should generally should not change the trans fluid in a high mileage auto trans that has not had fluid changed, with the idea being that the unit is so worn that it 'depends' on the grit in the fluid to work. If you swap out with new fluid the old worn trans looses that and can start slipping more. Is that true? Any personal experiences? I am not really looking for the "replace it with a new trans" answer, I am looking more for the GRM thoughts on the problem and the GRM budget fix. Thanks
Two things come to mind.
1) Debris is settling in the bottom of the pan and starting to plug the filter.
2) The front pump is running dry (clogged filter) or bad drain back valve.
Either way the future is not looking good for the trans 
.
Paul B
The new fluid in and old transmisin is just a rumor.
A fluid and filter change can often do wonders.
Worth a try.
After managing transmission shops for a few years, here is my guess.
Firstly, changing fluid can do more harm than good, and at the shop we never change fluid on a car with transmission problems. Our reasoning is that if it does make it start slipping, we could be liable for it if the customer makes a fuss. In the real world, if it makes things worse, you were due for a rebuild anyway, you maybe just accelerated the schedule a bit. If it makes it better, yeehaw.
Cold startup noise indicates a few things to me. The easiest explanation is that the filter is clogged and the cold, thicker fluid has trouble getting through and its starving the pump. Once it warms up it sneaks by the clog a little easier and the noise goes away. I would address it ASAP for two reasons. You have a variation on an A604 transmission. The pumps are not known for longevity in the face of grit. The planet assembly is also pretty soft and likes to give up the ghost as well.
Double check your inspection cover, too. Its possible that it has become bent and is contacting the flexplate or converter. That wouldn't explain why it only happens cold, other than its possible that the increased pressure could be flexing the plate more than when its hot.
The good news is that A604 (and variants) are relatively cheap to fix compared to others. At my shop I would get anywhere from $1400 for a plain-jane rebuild, up to $1800 or more depending on if the pump, planet, or other parts need to be replaced. ... and we were a pretty expensive shop. Those prices include R&R, converter, tax, everything. If you take it out and bring it to a shop, look for $600-900 for a bench build with converter.
