Why is my mouse acting up?

I recently changed the RAM chips in my MacBook, from two 1gb PC3-8500S-7-10-B1, the ones that come with the machine, to one 4Gb PC3-8500 and one 4GB PC3-12800. When I restarted my machine, the mouse started acting up by randomly moving about and selecting without me touching the track pad.

Does anyone know if this May be a consequence of my upgrading the RAM, or if it is more likely a problem with the track pad? Also, is it a problem that there are different serial numbers on the RAM chips?

I'd be greatful for tips! /Chris