over time all moving parts can develop different noises. These can be simply solved with a little bit of maintenance, such as adding lubricant.

Steps you can follow: 

1. Find the source of the squeak: Squeaks come from rubbing or friction between parts; so, look for moving parts (axles, wheel bearings, brakes, springs, the swivel mechanism). It’s probably a wheel or springs.  
2. Once you find the source, apply some lubricant (spray penetrating oil like CRC or WD40, or silicone) on the springs or axles or the swivel parts, etc. You might need to remove a wheel or axle, etc. That is easy. 
3. If the squeak is coming from the housing for the front swivel wheel, then push the keeper button underneath, then pull out the whole mechanism, (noting they are meant to be stiff!). Apply lubricant and re-insert, ensuring button is properly aligned and pops back into place. 

That should resolve the issue. We recommend a little of the same maintenance every now and then, to keep your product in top condition, and assist with long term use.