Being the service manager, I'm going to lay out everything at once for you so you can relay it more efficiently to the tech working on it.
There is a hydraulic tensioner that requires you to put it into a vice and put a "grenade pin".
There is also a mechanical tensioner that is a bearing/idler with two pin holes in it that work as an eccentric to further adjust the tension. This is the bearing that the hydraulic tensioner pushes on.
If the hydraulic (vice one) was the only one removed, we're good on that note.
If the mechanical tensioner (bearing with two pin holes) was replaced or removed for ANY reason, it needs to be set properly. If it is not set properly, you can get loud clacking type noises that sound from the rear, and it WILL toss the belt if it is in the relaxed position... This will lunch the engine.
So obviously find out if this tensioner was removed or not. If it was, you will need the special tool to adjust the tensioner while tightening the set bolt. Any Mitsubishi or Chrysler/Dodge dealer will have this tool.
If all is well on that note, make absolutely certain the timing is correct. The rear cam is a bugger to see and to keep set while installing the belt. If it is off two teeth it will make noise as it will lightly tap on revolution.
If all is well there, we can get on with the common problem and solution. I stated the previously clarifications not just because it doesn't hurt to check again, but also because the next procedure could cause damage to the engine if either condition mentioned was present.
As I stated before, it is very common for the back cam to slip during install, or require working back and forth to get the necessary play to slip the belt on. On this vehicle the automatic lash adjusters are notorious for drawing air during this process, even only rotating the cam 20 degrees back and forth 2 or 3 times. To resolve this you will need to do an air bleed on the system. This is very close to what you were attempting, just a bit more drawn out.
With all previous safety concerns regarding the belt timing and tension taken care, Start the vehicle and bring it warm or at least 3 minutes of idle time.
Then slowly rev the engine off idle up to 3000 rpm over the course of 15 seconds.
After the 15 seconds, release the gas pedal and let it idle for 15 seconds.
Then, again slowly bring the engine speed up to 3000 rpm over the course of 15 seconds
Release the pedal and let it idle for 15 seconds.
Continue this process until the noise is eliminated. It can take up to 30 cycles before it is completely gone, particularly if the vehicle sat overnight, etc, as well. Once it has been reduced satisfactorily, drive the vehicle and any remaining noise should disappear immediately.
This is something I need to do on probably 1 out of 3 Endeavors that I do timing belts on, and it is always the rear cam that kills you because of the tension on it when at TDC1.
Just be sure, and I can not emphasize this enough, that the timing is correct and that the mechanical tensioner was either NOT removed/disturbed or if it was that the tension was set CORRECTLY during final installation.
If you have any further questions, or need elaboration, please let me know. I am extremely familiar with this vehicle a I am the only Mitsubishi technician in a 75 mile radius of my area. I would be happy to assist you further if needed.