Snoop Dog and Twista songs with timeless synth line in it
 

I believe both artists used the same synth line, but maybe they're just very similar. I can't describe it.. it's kind of pitchy I guess. I can whistle/hum it and I have no problem embarrassing myself if that's how it has to be.

Found it! Snoop Dogg's is called "Aint Nuthin but a G Thang" and Twista's is called "Mobster Anthem".

Apparently the synth sound is well known and called "the west coast whistle".