OWINGS MILLS, Md. -- Baltimore Ravens coach John Harbaugh knows Sunday's game in Indianapolis is going to be louder than the previous road trip to Cleveland.

The Colts play their home games indoors, for one. There's also that talk about the Colts artificially amplifying the sound when visiting teams are on offense.

"Rumor has it, they pipe crowd noise in there," Harbaugh said Monday. "So, we'll see if that's the case or not."

When asked if that's illegal, Harbaugh said with a smile, "Yes it is. That's the rumor. Sorry, Chuck."

Chuck Pagano, the Colts head coach, was a Ravens assistant under Harbaugh for four seasons. So, call this a playful jab at his former defensive coordinator.

The Ravens are 0-2 at Lucas Oil Stadium, losing by a combined score of 51-6 against Colts teams quarterbacked by Peyton Manning. In those two losses, the Ravens committed 11 penalties. In comparison, the Ravens have been flagged for 16 penalties in the first four games of this season, one of the lowest penalty totals in the league.

That trend of reduced mistakes has to continue for the Ravens as they play four of their next five games on the road.

"The challenge is you got to go play another team in their environment," Harbaugh said. "That takes an incredible amount of discipline and poise. The more disciplined and poised we are, the more able we are to execute and tune out the noise."

How that noise is actually generated depends on whom you ask.