One definition of drivel is senseless talk or content. Dribble’s main noun definition, outside sports, is a small, unsteady stream. The words almost converge where drivel, in a secondary sense,means to slobber or drool (drool being a sort of small, unsteady stream), and this perhaps has something to do with dribble sometimes being used in place of drivel in the senseless talk sense. The mixup is common, but the words are generally kept separate in edited writing.
Examples
These writers use dribble where drivel would probably make more sense:
[I]t was a meandering ride into the unknown, coughing out sometimes dreary and mindless 30-minute dribble within the exasperatingly few sublime passages. [New Straits Times]
“Self-indulgent, whiny dribble,” wrote more than a few critics, while others praised the project as inspirational. [Best of New Orleans]
A few glasses of wine later, things really start to heat up, but before your frock hits the floor, your date utters the most disenchanting dribble you’ve ever heard [Province]
And here are a few examples of drivel used to mean senseless talk:
On telly, we had but three channels, mostly pumping out drivel to anaesthetise the middle-aged. [Telegraph]
Cherry-picking this kind of bureaucratic drivel out of a massive document is easy and unfair without more reporting. [Reuters Blogs]
Simply put, Obamacare has forced Romney to reveal how much 100-proof drivel he’ll swallow and spit out with a smile. [Washington Post]