these little coreless motors sometime suffer whats called "the yellow tape of death." the manufacturers of most of these motors use a little bit of tape to hold the windings tight, but sometimes if the motors gets warm, or even for just no reason, that tape lets go and jams everything up. its possible to take the plastic endbell off and remove the tape, but its a pretty time consuming (and sometimes painful) process. you can get replacement motors here: http://www.bsdmicrorc.com/products.cfm?catID=10005 scroll down to the bottom of the page and you'll see the selection for the 6mm pager motors. stock AA motors are 5.3 ohm, so i'd go with the 8.5ohm motors (MK06-8.5), as the 4.5ohm ones might be too hot for the AA's propellers. i'd buy two, and replace both at the same time, using one 8.5ohm and one 5.3 ohm will probably make it want to turn while flying. using 8.5ohm motors should give you a little extra flight time too.

nick