In psychology, "outside bias" generally refers to outgroup bias (favoring your own group) or the actor-observer bias (blaming outside or situational factors
Apparently the term has no single agreed-upon meaning.
When a company or a friend suggest that your stereo will be greatly improved and that the sound difference will be CLEARLY audible. That's your 'belief group mentality' creating a bias
A suggestion may create a bias. Or it may not. If you believe otherwise, that's a bias.