LIMA — While the standoff between the Peruvian government and guerrillas holed up in the Japanese ambassador’s residence here entered its fourth week, several photographers staking out the complex were startled in the early hours of Jan. 7 by what sounded like a gunshot.Scott Dalton, an Associated Press photographer who was on the roof of a house across the street from the residence, said the noise seemed to come from inside the compound and sounded like at least one explosion, followed by an echo or another detonation. Police said the mystery sounds appeared to be automatic weapons fire but said they had no reports of any injuries.For the previous five days, no hostages have been released. Seventy-four hostages remain under the control of guerrillas of the Tupac Amaru Revolutionary Movement, or MRTA, who are demanding that the government free hundreds of their imprisoned comrades. The last time the guerrillas released hostages was on New Year’s Day, when seven walked away.There was no sign Jan. 6 of Red Cross representative Michel Minnig or Roman Catholic Archbishop Juan Luis Cipriani, intermediaries in the crisis who have regularly entered the compound over the past three weeks. Red Cross officials other than Minnig, however, continued their routine visits to take in food and water.