Maxima blower motors fail

[Duaneclark]

Hi, I've recently encountered two different Maxima's where the blower motor shuts off, but the problem is intermittent, sometimes a bump in the road will turn the motor on or off. It's the same with two different Maxima's. Both motors run smoothly with no noise when they do run, so I don't think it's the motor itself. Is there a common problem that other's have encountered before? Would make it easier for me to diagnose. Also, fiddling with the switch in different positions doesn't seem to make a difference. Thanks