Hey there,
The only moving parts in the Wii U are going to be your Disk Drive or the Cooling Fan, and since it doesn't sound like your console is having issues playing games, then it's a cooling fan issue.
My advice if you're cool with it, would be to open the console up and try to [guide|55904|get at the Fan]. Make sure that it is clean, and is spinning freely in its housing. I'd also suggest that you replace the current Thermal Paste with some [product|IF179-096|fresh Thermal Paste].
I get that this question is a few years old, but hopefully if someone else is having this issue, then this can help them.
Best of luck to you!