In some cases, the clunking you are hearing is because of a broken or loose transmission or engine mount allowing the engine and transmission to move when your vehicle is shifted into gear or significantly changes speeds.
http://www.ehow.com/info_7747555_clunking-sound-transmission.html
Look and Listen for transmission problems on previous page. Problematic sounds that an automatic transmission can make continued... √ Banging or Clunking Noise A banging or clunking noise coming from the transmission or transaxle when the shifter lever is moved from Park into any gear is likely an internal problem.
http://myautomatictransmission.com/using-your-senses-to-detect-transmission-problems-page2.htm
If when shifting into drive, neutral and reverse clunking noises are heard, a torque converter is often to blame. The torque converter turns while the transmission is in park and neutral, therefore any noise from converter problems will occur while in gear.
http://www.mistertransmission.com/noises-when-shifting
Clunking, whining, buzzing, or humming can all be indicators of transmission problems. Components of an engine or transmission cannot make noise unless they are in movement. Even if a noise goes away when the vehicle reaches a particular speed it does not mean that the problem goes away.
http://www.mistertransmission.com/noises-when-shifting
It could be the u-joints on the drive shaft that are making the noise. When the u-joints on the drive shaft are bad, there is an audble clunk when you accelerate and when slowing down (basically the same motions you go through when shifting gears).
http://www.answers.com/Q/Why_does_the_transmission_clunk_when_shifting_gears
If the car makes a clunking sound when it is put into gear or when the gears are changed, this indicates a potential problem with the transmission. If the sound occurs when the wheel is turned, the problem is most likely with the wheel bearings.
http://www.ask.com/vehicles/car-making-clunking-noise-453d69cefb213e5e
Full Answer. If the car makes a clunking sound when it is put into gear or when the gears are changed, this indicates a potential problem with the transmission. If the sound occurs when the wheel is turned, the problem is most likely with the wheel bearings.
http://www.ask.com/vehicles/car-making-clunking-noise-453d69cefb213e5e
Problematic sounds that an automatic transmission can make continued... √ Banging or Clunking Noise A banging or clunking noise coming from the transmission or transaxle when the shifter lever is moved from Park into any gear is likely an internal problem.
http://myautomatictransmission.com/using-your-senses-to-detect-transmission-problems-page2.htm
√ Vibration A vibration can be caused by chipped or damaged gears inside the transmission. However, don't jump the gun hear because vibrations are most often caused by a bad U-joint (if your vehicle is rear wheel drive) or a badly worn CV axle if you have a front wheel drive vehicle.
http://myautomatictransmission.com/using-your-senses-to-detect-transmission-problems-page2.htm
A car making a clunking noise could have one or more of a number of problems, including problems with the transmission, exhaust system or wheel bearings. The first step to determining what is causing the sound is to isolate where the sound is coming from. It is also helpful to figure out when the sound occurs.
http://www.ask.com/vehicles/car-making-clunking-noise-453d69cefb213e5e
why is my transmisson making a clunk noise?
Your transmission making a clunk noise because of an internal problem, when the shifter lever is moved from Park into any gear.