The heater core has gone bad or possibly a hose leading to it or away from it has gone bad.
heater core
A leaky door seal or windshield seal
Blown head gasket.
water in passenger floorboard, where is the hose that would cause this?
A common cause for this is a burned out blower resistor. Tech JK --------------------------
A damaged heater core will cause coolant or water to leak onto the passenger floorboard.
There are many things that can cause vibrations in a 2000 Toyota Avalon. One such cause could be a bent rim and another cause for the vibrations underneath the floorboard is the engine.
When a brake line is leaking on the Chevy Venture the brake line should be replaced as soon as possible. A leak, however small, can cause hydraulic fluid to escape the brake line which will cause a loss in brake pressure. The brakes should be bled of air after the new line is put in to remove gaps in brake pedal pressure.
Water.
If you left the vent open, or if the vent under the windshield is full of leaves, it could cause rainwater to flow into the floorboard.
Usually the fuse is going bad.
loss of communications, many things could cause this from a bad ground, to cut wire, to a bad chip in the computer ecm