Dashboard vibrates/oscillates over bumps. Is this normal?

I have a very occasional rattle in my center display, it's small, but, irritating at times. It sounds like you have a possible problem. I'd take it back to a dealer and have it looked at. Your 2015 C should still be under warranty unless you have a 500 mile daily commute. I believe any Toyota dealer is obligated to honor warranty complaints so I would look for one with a competent body shop. That's my opinion for what it's worth. Good luck.

 

Are we sure this isn't the glove box squeaking issue? It sounds more like a rattle than a squeak.

 

In my case, I know it's not the glove box. If I push in on the top of the dash above the "idiot" lights the rattle stops. My rattle is occasional and for some reason occurs when I first drive the car. Either that or after a few miles I'm immune to the rattle. Regardless, it's a small price to pay in order to be driving such a great car.

 

Bumping this as my 2016 is having what sounds like the same issue (no pun intended). Just hit 34K miles and noticed that there is a rattle from what sounds like right in the middle of the dash, near where the windshield meets the plastic and the defroster vent. Sound is there usually on start-up, especially if it's a hot summer day, and then may go away as the day progresses. Only there when the car is in motion. Goes away when pressure is applied to the center-left plastic portion of the dash.


Took it to the dealership and they were not able to duplicate the issue so there was no fix...

 

I've had the same mid-upper-dash rattle on my 2013 since new. Irritating to be sure.
I've tried shims between the plastic parts and something squeezed under the overhanging piece of dash, but nothing has worked for long.