The blower motor may be failing or there could be debris caught in the fan.
does it have a ecotek valve fitted?
u joint
possible rear heater blower wheel has broken center hub!
Change the blower fan speeds to see if the noise changes. It is possible that the fan is still running while the heat is off, and the fan is rubbing.
wheelbearing or cv axle enjoy
When you hit the bump, the mouse wakes up.
Low coolant. If the coolant is low then the heater core is not able to transfer heat in to the car.
brake pads shot
Instualation of a heater core on a 1999 Ford Explorer V6, how do you install the heater core.
It could be differential bearings.
This is caused by a faulty heater core that has corroded and now has a leak. It needs to be replaced.
What causes ticking, check engine light, and the check gauges sensor to come on in a 1999 Dodge Durango 5.2L SUV?