Normal sounds. The one in my 6.0 does the same thing.....
A tip, if you find you need to replace the plug..... I’ve done this on all the block heaters that have needed new plugs.
When I had my Excursion parked outside, the cord I plugged into was plugged into a non-GFI outlet in the garage (since I didn’t want to have to worry about the outlet popping is someone sneezed near the truck). I got home one evening, plugged the cord in and went inside. Came out the next morning to temperatures in the 20’s F, turned the key and realized the WTS cycle was taking to long..... S**T...... Got the truck started, went inside and found the drop cord had been accidentally unplugged. I thought about getting a drop cord with a “pilot light” but they are expensive. Doing more research I found this:
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https://www.homedepot.com/p/Leviton...Dead-Front-Plug-Clear-R50-515PV-LIT/205165460
This replacement plug has a light inside the plug that shows power when it’s plugged in. So now no matter where it’s plugged in I have a light, instead of just the drop cord that has a light. This has saved me a couple times......