Sounds like a simple reese bass with a lowpass filter.
This is a nice simple reese to make:
https://www.youtube.com/watch?v=1C8ZN0vM8sYDo exactly what he does until around 1:30 but then instead of putting a double-notch filter on like he does, use a lowpass filter. Put the cutoff between 9 and 10 o' clock. This should give you the sound you want.
Hope this helps!
