I have owned City 2006 and Altis 1.8 2015. You hear knocking sounds when the fuel quality is bad. I have experienced that in both cars.
Solution 1: Change your petrol station to the one that's Company Operated AND reputable. Recently, a viral video showed PSO company operated pump at Saddar Rawalpindi to have water mixed in it. The staff at such company operated stations probably steals petrol and adds water or other oils to bring the level back up to the same level as before theft. So change the petrol station to a good one, and the problem will go away.
Solution 2: Mix Hi-Octane. Like in a tank full, you can ask for Rs. 1,000 to 1,500 of Hi-Octane, and the rest with normal fuel. Some experts do not recommend it, saying that it isn't a very efficient thing to so. However, it fixes the knocking sound problem.
Solution 3: Add a bottle of Octane Booster to your fuel. I have tried STP, Liqui Moly, Profi-car, and recently Bell 1. They all work well.
Warning about Hascol: I used Hascol fuel after I had issues with PSO (at Aga Khan Hospital, Karachi). It works wonderfully well; no knocking and good performance. But a friend in Toyota Indus asked me to stop immediately, because, as per him, Hascol fuel has additives which damage the engine in the long run. After about 1.5 years of Hascol, I went for Catalytic Converter's cleaning, and saw exactly what he warned me about: There was orange/yellow deposit on the converter.
Another advice: Choose a good petrol station, and then stick to it. All petrol stations are not the same, even if they are the same brand. I am now using the following fuel stations, strictly - no compromise:
Shell:
Shell at Nursery in Karachi (the big one, not the one near furniture market)
Shell at Super Market, Islamabad
Shell at Jinnah Super, Islamabad: Bad experience
Shell at Askari 4, Millennium Mall, Karachi: Backup only
Total
Total at Super Market in Islamabad: Best
Total at 2 Talwar, Karachi: No complains
PSO
F-8 Markaz, Islamabad: Good
Jhanda Chichi, Rawalpindi: No complaints yet, but I use that rarely
Karsaz, Karachi: Good
PSO House, Clifton, 3 Talwar, Karachi: Good
PSO Kh-e-Ittehad, Karachi: Good
