
Honestly. Happens a lot once rain and park grit get into the moving parts. First figure out where the sound lives. Push it slowly on a smooth floor with no music or TV on. Lift the front and roll only the back wheels and then switch. Spin each wheel by hand, squeeze the handle, click the brake on and off, and start to fold the frame a little. The spot that squeaks will give itself away.
Now for the quick fix with stuff you already have. Clean the wheel hubs, axles, brake parts, and any folding joints with warm soapy water and an old toothbrush, then wipe dry. Pull out hair and thread wrapped around the axles. When everything is bone dry, rub a plain candle or a dry bar of soap on the axle rods and where plastic meets metal. You can also scribble a soft pencil on the rubbing surfaces for a bit of graphite. Avoid cooking oil or heavy grease since they grab dirt and the squeak will return. For brake noises, clean the pawl and the little teeth on the wheel, then add the faintest touch of wax or soap there too. If a joint still chirps, snug the screws but do not crank them down, or slip a tiny piece of thin plastic or tape between the two parts to stop metal on metal.
Since you get a lot of rain, try a quick dry off after wet walks. Towel the wheels and metal bits, park it open indoors, and give it a short roll now and then so moisture does not sit in one spot. A five minute clean and a swipe of wax or soap every few weeks keeps it quiet. If one wheel feels rough or wobbly and the noise follows that wheel when you swap front to back, the bushing is wearing out. The cleaning and dry lube trick will stretch its life until you can replace just that wheel when the budget allows.