Reducing the Noise from Laundry Cart Wheels

Are the wheels squeaking as they turn, or is it the noise of the wheels on the floor? If it is a squeak, then a lubricate such as light oil or grease will do the job - WD40 is very light-weight, and is really just a water dispersant. If it is the wheels on the floor, then it could be that they are old and have gone hard and/or have a lot of dirt and grit embedded in them. Have you tried contacting the trolley manufacturer to get new ones? Also, if the wheels are loose, so rattle side to side, they can make a noise as well. Check to see if the wheels can be tightened up (and add a splodge of grease to them).

WD 40 should silence the squeak.