15mph the front end starts to whistle - 2003 Jeep Grand Cherokee

Whistling noise while the car is just sitting if often a vacuum leak in the engine compartment. Could also be a leak in the AC/Heater blower ventilation...and would cease when fan motor is turned off. Also could be a leaf or debris stuck in the recirc vent door causing air to leak by. Again, most likely to occur only when vent fan motor is running. The creaking noises (if while moving) is an indication of needing a front end lube job (normally performed during oil changes). All the rubber joints become dry and the vehicle will sound like a creaky old baby carriage with even the slightest movement of the vehicle body.. These are common issues, and give you a place to start investigating given the limited information provided. Best of luck resolving these issues.

could be wheel bearings a tire or cv joints,

one of the cabin seals has come lose or part of the plastic under the windscreen has a gap, can happen with plastic. just need to reseal the gap or refit it and seal at the same time. its body panel sealer can get it in a tube for a sealer gun or you can get the brush on type from most car part stores.

check the PCB balve maybe is cloged and the breather that create high vacuum wen are cloged and create a whistling sound.

Could be a front hub bearing or axle shaft.

well it may help if you open the hood, then start the car and see if that helps you locate the item which is whistling. many cars have a power steering pump which likes to whistle until it gets warm. generally this is less than 5 minutes, and that is more like a screeching sound. something is either blowing out or sucking in through a small orifice to make the whistle, you need to physically locate the source of the sound. many bearings are in there spinning and any of them can be doing a cold screech.

myself I have been know to use a BFS, which is a big long screwdriver, i touch the pointy end to each of the spinning components and put the handle end to an ear. yes this process is not suggested for people with long hair or just no damn sense. but as i move the pointy end from component to component i know immediately when i touch it to the screechy one.

i believe this to be normal, is it the turbo model?

Are the windows up tight and sealed?

try sticking your hand out the window while driving and cover up the seem on the side mirrors. ususally those make loud whislte noises

I assume that the noise changes with engine RPMs, not vehicle speed since you mention washing down the engine - something pretty hard to do if the car is going down the road-
Is it possible that what you describe as a squeak is instead a whistle? The symptoms you mention related to water could mean that an intake manifold gasket (or another part of the intake system) has a bad gasket and is causing a whistling noise from air being pulled in where it shouldn't happen. If the failed gasket is allowing water into the intake system, that would explain why the engine sounds like it wants to die. 
You might take a 2-foot length of vacuum hose or similar, hold one end to your ear and move the other end around the engine to see if you can more accurately isolate the source of the noise, be it squeak or whistle.    Obviously, don't hold the hose too tight in case you get tangled up with a belt or rotating part.
Good luck-