YTH24V54 Riding Mower. High pitch whine when brake pedal is released.

SOURCE: High Pitch whine during acceleration

First you need to isolate the noise. You don't mention the mileage on the car. Do you have the supercharged engine? If you do, remove the belt for the super and make sure that is not the problem. If you still hear the noise approximately below or from the super area, it is most likely the belt tensioner pulley.
In my car there was a large washer over the pulley (original equipment), as the pulley wobbled on the bad bearings, it would cause a sound like a bad alternator or gear whine getting exponentially worse the faster the engine reved. Now that the part is replaced, you can barely hear the engine idle and is significantly quieter at high RPM.
My car - 2004 Pontiac Grand Prix GTP with 66,000miles.

SOURCE: A high pitched whining noise in the engine.

This Noise Description sounds Indicative of the Sounds that come from the Serpentine Belt Or Related parts such as Belt Idler Pulley or Belt Tentioner witch also has a Pulley, but if Tensioner itself is Literally BROKE I've replaced a number like this it will cause a Whining noise . Best case scenario its just the Belt, and if any of the other Problems turn out to be the Culprit the Belt MUST be Replaced Anyhow as Damage is Being caused By the Very Whining you hear.
PLEASE Spend the Extras $ for the BEST BELT as this Drives your Water pump, Alternator, A/C Compressor, Power Steering Pump All Crucial to Control of, easy Steering ,All Electrical-Power Distribution, The COOLING of Engine << VERY CRITICAL Component
The Pulleys usually have a more Hum type Whining. So I would say at Best The BELT , And WORST Belt Tentioner is Broke

SOURCE: High Pitch whine during acceleration

Hi Pullerwife,

I have a few suggestions for you,

First of all, check your air filter, make sure its clean, not clogged, and doesn't need to be changed.

I don't know how handy you are, but if you are fairly handy, check the idler pulley bearings, if your not, have a shop check it out, as a last resort.

Power steering pump/fluid being low is also a possibility, but thats usually more of a lower pitched whine then what you describe.

You say once the vehicle is warmed up, the whining stops. Does Weather seem to be a factor as well?

Hope I've helped, and don't forget to rate.

Lazaruselite

SOURCE: I have 16 hp Craftsman riding mower with a Kohler engine.

It may think you are in reverse and is killing the motor to keep you from backing up with the blade running. Look for switch that is telling it when you are in reverse, maybe it is stuck with grass or other debris. another possibility is that the blades are jammed and they are stalliing the motor. Mines stalls easily when cold.

SOURCE: riding mower won't pull uphill

your drive belt is stretched out it gets hot and slips the most torqe is on hills