Here is my solution!

I had exactly same problem as you before. Landlord manager ignored my complains for several months. However, a clerk in Dept office secretly told me to go city government, and find Environment Control Office to complain. I called once and an office came to my apt to measure Noise level (fB) in different locations and found one location is over city law limitation: 50 fB. He said this is violation of city law and asked landlord immediately to fix it. A few workers changed springs (replacing old springs) in next day and my apt was quiet. Landlord then asked the city office to measure fB again. Case is closed by city official.