'98 Voyager

Almost 150000 mi, 2.4L engine


3 days ago. The car started having brake trouble

Whenever the brakes are fully depressed after driving for about 20 min, the (It's hard to tell which) front or rear brakes start grinding heavily. It is enought that you can feel it throughout the whole car.

The brake pads on the front were changed about a year and a half ago, and about 2 weeks ago my dad and I did the struts on the car and the pads were still in fairly good condition (the brakes have been changed 3 times by us, so we have a good idea of what good pads look like). We changed the fluid about 6 months ago, and checked the rear rotors about 8 months ago (they looked fine).

Therefore, I am stumped and wanted to know if there is a problem with the brake system that we probably don't know about, or is it something else?