Droning noise/Harmonic sound

[dash1979]

Hi,

I've got a 2007 yaris, 255,000KMs.
Just replaced Front Wheel Bearings & Rear Wheel Hubs/Bearings.
New Front Rotors and Pads over the last few months.

I've got a 45min comute to work. After driving 30-40mins the car starts to drone. could it be a tire heating up or a bad belt? Tread pattern wear? There's no vibrations. Tire PSI's all equal.

Car drives fine, steering wheel is smooth. Rear brakes are adjusted and wheels spin freely and parking brake works properly.
Front calipers are not seized. Even after my drive home all rims are cold, drums are cold, front rotors warm but not too hot.

I think my water pump is gone because my rad fan kicks in every month and i fill up the rad(half jug of coolant) and the fan goes away. I've tried filling the reservoir and it just stays empty or sucks the coolant out.

The noise comes in and out at all speeds. faster 110KMs and up. And stays audiable after 30mins of driving.

Driving down a steep hill i put car in neutral, the droning sound is still there.
sound is there with clutch in or out.
Then I'll hit the brakes in neutral and it slightly goes away.

It's always strange that it takes time for it to start which has me stumped.

Any comments or suggestions greatly appreciated.


Thanks guys/gals, jp