Very strange noise

[Eric4wd]

I take it this is due to the fact that it's been butt cold lately (-22F without wind chill factor) here in eastern Canada. Nonetheless I'm still trying to figure out what the heel is this noise. It happens unexpectedly while cruising (not speed dependant). It is a loud HUM coming from the middle of the dashboard and I would say near the firewall. When I shut off the ventilation, it goes away. Conversely, If I leave the ventilation on and come to a complete stop, the noise goes away too. When I accelerate and hit around 30mph, the noise reappears. Anyone had this happened before? It's a 2002 Seq limited with 22K miles.

[peid]

Don't have it but sounds like your condenser.

I believe Toyota's condensers turn off during hard acceleration to prevent loss of power when needed.

This would sound likely as you indicate it also goes away when you turn off your system.

It can vary depending on your speed at do it throughout the entire speedometer. Depending if your truck shifts out of the gear to a different gear to gain more power.

That is my guess.

[Eric4wd]

Isn't the condensor only working with A/C? Mine was switched off when all this happened and I wasn't accelerating hard either. Sounds like there's a motor somewhere feeding the heated air into the cabin that is about to give. It only happened twice this month so it'll be hard showing this to a service rep.

[peid]

The condenser is also working with either Defrost modes.

It doesn't require pedal to the metal acceleration, just enough to maybe kick it out of over drive.

Like I said, I don't know for sure, but that is what it sounds like to me.

[Bbbutch]

Probably not the problem but you should still check to see if the weather strip that goes accross the top of the fire wall and makes contact with the back of the hood is still in place.

[Brian M]

Are you 4wd? Some have had a noise emitting from the front dif.

[Stooge]

The Tundra sometimes makes this noise as the AC compressor cycles (AC or defrost mode). Sounds almost like a circular saw. It's actually the refrigerant throttling through the orifice in the condenser. My charge was OK and everything works fine, so I have learned to ignore it.