In case yours is a Frontier EE cart...you can order wheel bearings from them for $2 each, last I looked. I had to replace mine after years of use; it was more of a 'grinding' sound, as I recall, though. I have used silicon spray when I've heard squeaks that were hard to pinpoint. It will probably have to be redone periodically, but at least, it doesn't attract and hold dirt/dust.
Margo