Run the noisey engine on a loop of track. Run in one direction at slow spreed for about 20 to 30 minutes. Repeat at half speed and then full speed. Then do the same with the engine running in reverse. This should quiet down the loco. Then check to make sure the gears in the truck are LIGHTLY oiled with a plastic compatable grease.  Joe

What type of track are you using?  Joe

If you are using DCC you can run the two trains in opposite directions. If you're using DC you need special wiring. Either way you will need a throttle for DCC or power pack for DC for each track. DCC is the way to go because it simplfies wiring.  Joe.

Go to Soundtraxx web site. On the bottom right click on manuals. Click on documents for factory installed decoders. Scroll down to Bachmann. Click mon the loco you want and it lists the CV# and what they do as well as factory setting. Chuff rate is CV116 I think and is default value 75. Change this to a different value. Try increasing the value by 5 (IE 80) run the engine. If it gets closer to being in synch, change it higher by 5. If it gets worse, change it by subtracting 5 from the default(IE 70). There might be a formula for figuring this out with out trial and error. Google steam decoder chuff rate. Hope this helps.  Joe

The decoders in these units should be dual mode. They will work on DC or DCC.

Several thing I would check: take off the body on both units. Chech the wires to the decoder to make sure they are all attached and no strands are touching another wire next to it, take the weight out and check the wires from the trucks to be sure they are attached. Also is this part of a reverse loop or y track? If yes it could be the auto reverser acting up.  Joe

Down load the Soundtraxx Diesel users guide from their web sight. One thing to try is to program the decoder to use a speed table. I think it's CV25. There are 15 factory ones pre set and a user adjustable one. Also if your lay out has a continous run run the loco in one direction for about 20 minutes at slow speed. Increase the speed to half and run 20 minutes or so. Then run at top speed or close to it for another 20 minutes. Repaet the above running the loco in reverse. This helps break in the drive train. I use a Digitrax PR3  with Decoder Pro to program my Tsu decoders. I set up a speed curve to limit the top speed. This is a great program to use.  Joe. 

Since you mentioned a UT4 throttle,I assume you're using a Digitrax system. With Digitrax, a short will cause the system to beep several times and shut off the power to the tracks until the short is removed. If you hear no beeps when the loco stalls, it's not a short bbut probably a track issue. If the problem only happens with one loco and not runnig both together, the second loco might have all wheels contacting the track and pushing the lead loco. Once past the spot the lead loco will then pull the second one over the bad spot. Just a thought.  Joe.

 Do you have a volt meter? If so can you measure the out put of the plug on the power supply? Or check the power at the rails with no locos on it. If the power is over the limit of the decoder, I suspect the power supply is bad.  Joe. 

Look in the last issue of Model Railroader. Fred Miller did an article on adding sound to a trolley. The decoders he used are Digitrax. He created a sound file that can be loaded into Digitrax sound decoders. These can only be done using a Digitrax PR3. This might be a good article to look at.  Joe.

Remember: it's your railroad. What you consider great others might find boring. It's all about having fun.  Post photos as you get going.  Joe.

Sasha, since you are doing DC controll, how are you going to controll all the trains? You will need a power pack for each track. With DC if you  power all the tracks with one power pack, all trains will travel in same direction at the same speed. Joe.

Try CV8=8  Joe.

It could be the gear/fly wheel part on the motor shaft is loose. If you can dissasmble the loco,  take out the motor, hook up power leads to it apply power and see if the motor will still spin when the fly wheel is held. If it does, this is the problem.  Joe

Did you give it a 2 or 4 digit address? 2 digit address on most dcc systems are 01-127. 4 digit is 128-9999. Also what system are you using? Try address 3 as some times sound decoders are a pain to program. If address  3 works, the decoder was never set to the new address.  If not try a decoder reset. Usually CV8=8  will do it.  Joe