If your vehicle is showing whining noise from the bottom of the engine that rises with rpm, here are the most likely causes and the parts you'll need to fix each one.
Low transmission fluid or a worn transmission front pump causes a high-pitched whine from the bellhousing area (bottom rear of the engine) that increases directly with engine speed.
While technically an accessory, the A/C compressor and lower idler pulleys are often mounted at the very bottom of the engine block. Worn bearings here will whine loudly as RPM increases and the sound easily travels.
A restricted oil pickup tube starves the oil pump, causing it to cavitate and whine from the oil pan area. This is frequently caused by engine sludge or excess RTV gasket maker breaking off inside the pan after a recent repair.
If the engine timing components were recently serviced, an over-tightened balance shaft chain or oil pump chain will produce a distinct, supercharger-like whine from the lower engine block.
Internal bearing or stator failure inside the torque converter can create a continuous whine from the bottom rear of the engine that scales with RPM, often accompanied by shifting issues.