I have a Toyota T100 1996 that has a noise coming from under the passenger compartment but only in cold weather. I seems to be related to the drivetrain and possibly the speedometer cable (just a guess). What possible items could have a cyclical noise based on speed. Doesn’t matter if the clutch is in or out, but when I let off the gas, the noise changes pitch slightly. After driving for a while, the noise goes away.
Could be a failing blower motor, try turning off the fan or adjusting the speed of the fan and see if changes.