Puzzle; Reefer Smells Rancid

So here is a odd one we're trying to figure out. Drop a clean (inside) reefer off at customer drop lot for loading. Remotely turn it on the night before its scheduled to load to ensure its precooled for them. Customer emails to tell us the reefer absolutely stinks and will not go near it.

Send driver to investigate; reefer inside is clean and good. Driver tells us he can't get within 10 feet of Reefer engine as it is absolutely rancid. What happened?

I assume an animal such as a racoon or squirrel climbed in, and got ripped to pieces when the engine was remotely started. And now that is has been baking in the sun all day... Only logical thing I can think of. You guys have any thoughts?

FYI we're trying to figure out how to move it. No driver wants to touch the thing. Can't call pest control to the customer (food shipper, bad optics). Lol I'll post updates as this unique situation develops.

 

We dropped it at another terminal, it magically doesn't smell anymore but we did remote turn it off. So we asked shop to run it and see if the smell returns and to investigate lol - still a mystery

 

Shop can not replicate or identify the smell. The issue will always remain a mystery lol