There was a road construction in front of my apartment when I was tortured, which actually started long before likely in the middle of 2011. Although, it had continued for more than a year, which was unlikely in Hong Kong unless it was a part of the intelligence operation. The construction was quickly completed there in general and it just needed weeks to be done for fifty yards.
The construction noise was surely noticed before my realization of the spy operation, though it was not out of the ordinary. It might be a planned renovation originally but availed to the operation from the middle.
This drilling sound was critical to my mental, as all of the windows of my apartment was open due to the threat of carbon dioxide suffocation. It was so loud during the daytime from Monday to Saturday that my nerve was irregularly stimulated. As you can see, it was quite a limited place that you could drill within its fifty-yard length, though it would not stop at all.
The construction was halted during the night, though I got other noised from the upper room, therefore some noises were always out there in turn, which deprived my energy as well.
I assume this should be one of the general methodologies of the intelligence operation. It was just a construction and there was no more meaning, though if you were a subject of the government authority and the construction continued more than it normally needed, it was meant to damage you mentally and physically. It might be an escalation of the paranoia, but it was enough to harm you as you doubted its true nature.
Furthermore, they could separate the noise teams for a dayshift and nightshift, which enhanced their operational capability. This continuous noises definitely demolished your mental after sleep deprivation, which was why they continued it until the end.