I have a 2017 RWD 2.5 turbo model with 35,000 miles. Under hard breaking I can sometimes get what I will call a groaning sound from the back of the car, at least I think it is. It will not happen all the time and there does not seem to be any issue except for the sound. I can not make it happen all the time. At one point I thought is might be a heat shield but I don't anymore.

Any thoughts?