2013 fast blinking turn signal

Thanks for all of the responses. Visibly there is nothing wrong from outside the car - every bulb is lit normally and lights up when it's supposed to. For me it's the passenger side, and there are no visible bulbs out - the parking light and blinker appear to be working and the correct brightness. I will try replacing the front bulb anyway, I know filaments can break and lay on other filaments inside the bulb, so it looks like they are working normally but in reality they create the wrong resistance so you get the fast blink.

Will update, hope to do the front bulb this weekend. Thanks again all!!!

Just to update this topic - I never did replace the front bulb. I had a bunch of moisture and occasionally water sloshing around inside the rear pass. taillight housing. I drilled two small holes near the front-most part of the bottom of the lens (above the rear tire, close to the back door) through the clear, and let the water drain out. Problem solved! Hasn't fast-blinked since then. I used a small drill bit, approx. 1/8", and didn't see any issues over the winter. No more water inside the housing, no more fast blinking turn signal! Still using the original front bulbs.