1994 Toyota Pickup whirring noise appearing to be coming fr

A chassis ear that can be randomly placed throughout the vehicle while it is driven can isolate the noise. If it can be reproduced with the wheels of the ground and run up, you may be able to locate it as well. The fact that it is present on accel and decel suggests possibly a differential type noise, pinion bearing or side bearing. If this is a manual transmission, it could be within that as well. Does the vehicle have a canopy, and sliding windows? Sometimes when it is driven with the window open, the sound can be amplified from the rear and determined. Draining fluids and inspecting may also give an indication.

Chassis ear is a device made by a company named steelman. It has sensors that can be mounted throughout the vehicle that report to a central switchbox, and through the use of headphones you can switch to each sensor and listen to the noises.