Liquid leak

No, there's definitely nothing in the rack that should contain liquid or leak!

I would start by shutting down the power to the rack, removing all the modules, and see if you can determine where it's coming from.

Sometimes electricians may use a lubricant while pulling cables through a conduit, so it could be that. The other possibility I can think of is that because the rack sucks air in through the front with the fan, if there's a vaporized oil in the air (e.g. haze or fog fluid), that can condense on the inside - I've seen that happen, although never enough to drip.