Blower Fan shutting off

So in my shop I have a wood burner with a HVAC blower hooked to it to blow hot air out. There is no thermostat, speed is controlled by a light dimmer switch. Had a different blower with this same set up on this burner for years, only replaced it because the old blower came apart finally.

What it’s doing is when it’s turned on it will run normally for maybe 3 minutes then it will stop spinning but make a humming noise for maybe 5 minutes then it will take off on its own again, run great for 3 more minutes and restart the process. This is not a new issue with this blower, been doing this since the day I got it. It’s like there’s a duty cycle on it or something. The fan is open on the side and while it is in humming mode you can spin it freely with your foot and there’s no resistance or catching.

I’ll post a make and model number tomorrow but any ideas in the meantime?