Take the filter apart, remembering how it came apart, so you can put it back together. That last bit will be important later.
The impeller is a round magnet with a hole through it. It spins on a ceramic or metal shaft. Ceramic on expensive filters, metal on less expensive filters. Not just the cheap ones.
Some impeller shafts have rubber or plastic bearings on either end. Some - which will wear through the body - have no bearings. On those the shaft spins in a dimple in the plastic filter shell/body.
The impeller assembly usually spins in a cavity or well. One small piece of gravel, stiff plant stem, or clump of algae can stick between the impeller and the cavity - tight enough to stop it up completely. Less than that can cause noise. Or worse, break off a bit or a complete vane from the impeller.
So, while everything is apart, clean all the bits with an old toothbrush and water. Flush out the impeller cavity. Re-assemble with care. Consider using a tiny bit of food grade silicone lube, or a tiny dab of petroleum jelly on the shaft. Make sure the impeller spins freely on the shaft.
After it's all back together, hang the filter on a tank, fill the filter with water, plug in. If it makes a screeching noise, take it back apart and figure out what is rubbing on what. Or you didn't get the shaft centered in the bearings so something is too tight.
If it makes a rattling noise, the impeller is loose.
It may be you got pieces from two filters mixed up and the shaft is the wrong size.
Or you mashed a bearing so much it wobbles a tiny bit.
if there is still a noise, record it and upload the mp3 so someone can help with diagnostics.
