I have a 1997 Honda Accord with automatic transmission and about 150K miles on it. Frequently when I accelerate to around 3000 RPM or higher, and then let go of the gas pedal, about 1 second later I will hear a thump/thud noise from the rear of the car. It doesn't always happen when I let go of the gas pedal, but it is more likely to occur if I have accelerated to 3000 RPM or higher.
You can hear the sound in this video - wait until the very end to hear it.
I recently took my car to my mechanic and had him look at a few issues including this thud/thump noise. He called me and reported his findings. He said that the thud/thump noise was just due to the transmission getting old, and it isn't a problem for now. But he said that down the road I'd have to either get the transmission replaced or get a new car.
When I went to pick up the car, I tried to have him clarify what he meant by "down the road" - did that mean one year or several years? He changed his mind and said it wasn't a problem at all, and I didn't need to worry about replacing the transmission or getting a new car. He said I could continue driving the car for several more years.
Based on my description and the video, does anyone have any idea what is causing the noise? Is it indeed due to an old transmission and there's nothing that can be done about it, and it won't be a problem short term or long term?