Interior blower motor works intermittently, 2000 s80

[Mojobaby27]

My AC and heat blower works intermittently. If I give it a good whack under the glove box when it's not working it will start working again. I changed it out, the blower motor and the resistor a year ago. Now it's doing it again. When I had it out originally it would work fine on the floor and then when I put it in the car didn't work. So I went ahead and changed the resister and it started working. And it ran for a year. It makes me think there's some sort of grounding problem but I have no idea where to start?
Any ideas what could be causing this? Thanks in advance for any advice.