Jason Hammel (8-6, 3.43 in 2012) has struggled, posting a 7-5 mark with a 5.03 ERA. (Patrick Smith/GETTY IMAGES)

The noise is a mainstay of the Baltimore Orioles’ Camden Yards clubhouse: the constant “pop” of a ping-pong ball bouncing off a table, a paddle and (sometimes) the table again, punctuated by roars of joy or eruptions of frustration from participants or onlookers.

The Orioles play table tennis pregame and postgame after both wins and losses, a display of Baltimore’s rare chemistry and the casual certainty each player has in the efforts of his teammates.

In that tight-knit clubhouse where long-term confidence outweighs daily doubts, no one seems too concerned about the struggles of an Orioles starting rotation that has at times been more consistent on the ping-pong table than the mound, a departure from the late-season dominance that carried Baltimore to the American League Division Series in 2012.

While injuries have forced the O’s to use 13 starters already this season (they used 12 all of last year), the core is largely intact. The lone exception is the addition of Scott Feldman, acquired from the Chicago Cubs on July 2 in a deal that included fellow starter Jake Arrieta.

None of the returning starters are performing at their 2012 level, though the numbers aren’t too far off.

Wei-Yin Chen, who pitched a staff-high 1922 / 3 innings last season, hasn’t really had a chance, having missed the better part of two months with an oblique injury. Chris Tillman (9-3 with a 2.93 ERA in 2012) is 11-3 with a 3.95 mark this season after winning Friday night.Miguel Gonzalez, who shut down the Yankees in a thrilling ALDS Game 3, isn’t far off from last year’s pace at 7-3 with a 3.48 ERA.Jason Hammel (8-6, 3.43 in 2012) has struggled, posting a 7-5 mark with a 5.03 ERA.

But as a whole, the rotation’s numbers tell a different story:

Baltimore’s starters had a 4.76 ERA through Thursday, fourth worst in the majors. They had surrendered 288 runs, four fewer than the woeful Astros, and given up 88 home runs, by far the most in the majors.

The cozy confines of Camden Yards may play a role, but the team has played in the park since 1992.

It’s not bad luck; opponents are hitting .287 on balls put in play against O’s starters, right around the norm. They haven’t changed their approach much, either, throwing approximately the same percentage of fastballs (60 percent), curveballs (10 percent) and change-ups (9 percent) as they did in 2012.

So what’s the issue?

Coaches and starters agree it’s “consistency” and “execution,” both maddeningly nebulous concepts. How do you fix inconsistency?

“It starts with having the same five guys,” Orioles pitching coach Rick Adair said. “The injury to Chen, which was huge — he was the only guy coming into this year who had pitched 200 innings. . . . We haven’t had anybody that’s ever done that.”

Though only one starter can take the mound on any given day, Hammel agrees that “finding a rhythm” as a rotation can make good pitching, like hitting, contagious.

“It’s more or less kind of just follow the leader,” the 30-year-old right-hander said. “With starting pitching, when guys are going good, it’s always one-upping the guy before. If we can build a little bit of a friendly competition, one person’s start can make it happen.”

That already may have started; Chen and Gonzalez turned in back-to-back gems against Texas this week before Tillman beat Toronto. But the Orioles aren’t just sitting, waiting and hoping to get on a long-term roll.

Adair and the starters are constantly discussing the aspects of the game they can control — mind-set and approach — in order to create more consistent performance.

“What are my best options? What’s your thought process? A couple of years ago we had a fine: If you had two outs and nobody on and the count went 2-0, you owed me a dozen golf balls,” Adair explained. “They’re being smarter and starting to understand things.”

A smarter O’s rotation would be scary for the rest of the American League; the Orioles already have 50 wins at the break for the first time since 2007. But by all accounts it has been the Baltimore bats that have sparked that success. The Orioles, through Thursday, ranked fourth in the majors in runs scored (444) and hits (858) and fifth in team batting average (.266). Their major league leading home run total (125) was 13 higher than the second-place Blue Jays.

“We’ve had different parts in the first half step up. . . . It’s a sum of all parts,” catcher Matt Wieters said. “It’s being able to not have one group carry the team. The offense has definitely been able to have a good first half, the bullpen has been strong again and the starting pitchers have shown glimpses.”

So for Baltimore, in third place in the AL East at 52-42, there’s no question where the additional push will have to come from in the second half.

“As a collective group — you can ask any of us — we definitely underachieved,” Hammel said over ball bounces and shouts of a heated set between Manny Machado and Troy Patton on the ping-pong table a few yards away. “But if you look at our record, you wouldn’t know it; I think we’re better than we were last year at this point. So I think our best baseball is yet to come.”