While on a road trip, my car started making a loud grinding sound (low pitch) when I slow down, even if the brakes are not applied. At 2 different instances (luckily close to home) the brakes actually seemed to fail - my foot went all the way to the ground with no response. I’m not sure if related, but my "service 4wd light goes on periodically and the last time I was in 4wd it took some time to get out of 4wd - it wasn’t responding to the 2Hi button. The car is a 2001 Chevy Blazer with about 160K miles.
The sound is there on acceleration also and seems to go away at higher speeds (maybe over 15-20).
Take this vehicle to a mechanic NOW. Brake problems are nothing to fool with. If the brake pedal goes to the floor you shouldn’t even be driving. Have it towed.