Improper sealing of the valves of the engine. The engine's piston rings may not be sealing correctly. The cylinder head may be loose or the head gasket might be blown or damaged. Usually this happens when the engine overheats or is run low on oil. On a two-cycle (2-cycle or 2-stroke) engine, check to make sure that the exhaust ports are not blocked.
The torque converter housing is mechanically attached to the engine's crankshaft causing the pump to operate whenever the engine is running. It's why a worn or faulty pump makes a whining noise in all gears, including park and neutral. A restricted or clogged transmission filter makes the same whining noise as a faulty transmission pump.