How often do you check you bearings?

Thanks for all of the input. Just to follow up, Neu recieved my 1512 on Tuesday afternoon and they put it in the mail back to me Wednesday afternoon. I also ordered a tube of 10 replacement bearings. The charges where $60 total. ($30 for the bearings/ $30 for repair and shipping) I would say that's pretty good all around. As far as how often the bearings need to be changed, they recommend replacement as soon as the bearings make any noise what so ever. I will start removing my motor every 5 packs from here on out.
Thanks again for your input.
Brian