That noise, together with the relentless wail of car alarms, is a reminder of the drugs and crime problem that is blighting one of Europe's most successful cities.
In the past decade or so Dublin has undergone a transformation. Thousands of young, working people have been lured to the inner-city by flats at affordable prices. But the renaissance is being threatened by drug addicts. In prosperous commercial areas, every shop has security staff on the doors.
In Patrick Street, the small convenience stores opposite the Protestant cathedral have their own doormen, while local newsagents weary of "jumpovers" - where robbers leap over the counter to get at the till - invest in closed circuit television.
And there are the stories of sheer horror. One shop worker - one of 2,200 people who reported attacks or threats of such attacks in the city in 1996 - was stabbed by a robber armed with a blood-filled syringe. For weeks while he waited for the results of blood tests he was terrified he might have Aids. "I was a nervous wreck," he said. "The guy that did it to me is dead now. He died of Aids two years ago."
The violence is not restricted to robbery. Alan Byrne, 27, a rehabilitated addict, was shot three times in the lower back in an assassination attempt last Tuesday in the Coombe area as he set off for work.
Byrne shared a flat with Josie Dwyer, 41, a HIV-positive heroin addict. They were together on the night in May 1996 when Dwyer was repeatedly attacked and eventually beaten to death in an apparent vigilante mob attack.
After two decades of an escalating drugs problem, the tactics of Dublin anti-drug vigilante groups are uncompromising. In the Sundrive area late last year they put up posters listing names of drug dealers to be shot.
As if this were not enough, there are savage internecine "turf wars" between dealers. "Cottoneye Joe" Delaney, 54, an alleged ecstasy dealer, is accused of the torture and murder of a dealer Mark Dwyer, 23, in December 1996.
Similar levels of violence surrounded the operations of PJ "the Psycho" Judge, a criminal with suspected INLA links, who tried to take over Dublin's cannabis market in 1996. Judge, 41, who was shot dead two years ago, was suspected of killing five rivals.
One of his suspected victims was William "Jock" Corbally, whose body was never found. He reportedly had his teeth pulled out, was beaten with a shovel before having his throat cut, then thrown into a lime pit in Co Kildare.
But dealers are willing to risk such violence for a share of a burgeoning market: According to the most recent figures, Dublin now has around 13,000 regular heroin users, up from 8,000 to 10,000 two years ago. Officers based at the Garda headquarters in Dublin's Phoenix Park believe that heroin is now responsible for 80 per cent of the city's crime. Their studies suggest addicts commit 85 per cent of aggravated burglaries, 82 per cent of muggings and 84 per cent of theft from cars.
As with Dublin's population, the profile of the heroin users is largely youthful. A recent survey carried out by a government task force suggested that 72 per cent of heroin users were male, 83 per cent unemployed and 69 per cent lived with their parents. Two-thirds of those regularly using heroin in the city are under 25, and almost the same proportion left school at 16 or younger.
Tony Geoghegan, director of the Merchants Quay Project which treats drugs users, said 900 mainly young, first-time drug users sought treatment in the city last year. A high proportion of these had begun injecting in the last six months.
"You are dealing with high levels of educational disadvantage and poverty, with few having aspirations," he said. "[They come] from areas where there is an established black economy and where maybe the parents were involved in crime or drugs."
The Irish government has tried to deal with the Dublin's heroin problem. In the early Eighties it used undercover officers whose efforts, accompanied by community action, were effective in tackling dealers who were then less careful about distancing themselves from the product.
And after the1996 killing of journalist Veronica Guerin by drug dealers, a murder which prompted an international outcry, the Government poured more funds into anti-drugs measures. A new Criminal Assets Bureau targeting major dealers was set up.
But as fast as the Garda act, so new dealers move in. The deaths continue, the estates built with short-sightedness in the Sixties continue to be littered with syringes and glass from smashed up cars, while the problems spill over into the newly gentrified areas where the residents are woken at night by the sound of helicopter blades.Reuse content