Loud and HOT radon mitigation fan
There are 2 types of Radon mitigation systems: 1) gravity, and 2) forced air. 

1) Typically a gravity system will be installed, with an option to install an exhaust fan at a later date, if the gravity system is not effective. 

2) After the gravity system runs for a year or so, additional readings will be taken to determine if the system is effective and has reduced the radon level. If it hasn’t, then an exhaust fan can be installed to “assist” with the mitigation (air flow) process. 

It sounds like someone has determined an exhaust fan is required. First, I’d try to determine if the fan is required. 

In both systems, air “intake” is required. That is to say, in order for air to flow through the pipes, there needs to be a way for air to flow into the system. So, in order for your fan to exhaust air there needs to be air allowed into the system. This intake air is called “makeup” air. (Without an intake, it’s like putting your finger over a straw that is full of water. If air can’t get into the straw, then nothing can flow out of the straw.)

Your fan could be overheating because it is unable to get “makeup” air. Did the contractors forget the makeup air intake?