Anyone else get a thump type sound the instant the voltage drops when the grid heaters kick in and then out?

 

It's the solenoids used to give power to the grid heaters. Very typical.

 

At times it's like I get rear-ended or something. Scares the **** outta me. It's very obvious and loud. The engine surges as well. Kind of gives the impression that it's a POS. Other times the voltage just drops and comes back up without making a sound.

 

This is soon after startup I assume? just sitting in park? I have experienced this too and there is another thread about it, I will try and find... I believe the consensus was that it only happens when the fan is on.... ac or heat, but the thump is from the fan.... dont know if its the same as what you are hearing.

EDIT: that took some digging, but found the thread I was looking for:
https://www.dieseltruckresource.com/...d.php?t=165768