I was wondering if I were to buy a house and put down $100K in cash that wasn't in any of my bank accounts, would that look suspicious?

Or, how about if i were to pay off a $30K car loan in 5 months, when I don't even come close to making 30K in 5 months at my current job. Does that kind of thing raise flags somewhere? This is just hypothetical, but I was just wondering.