I am driving a seven-year-old Japanese car. I observed recently that when the vehicle is stopping, there is a "tuck tuck tuck" sound coming from the engine compartment or front wheels. What is the cause and what are the consequences? Is the problem serious or should I wait till it is more obvious to do something since the car behaves normally at other times?
This is not an uncommon problem and is caused by an excessively worn brake disc.
Usually, when the disc is badly scored (grooves on the surface) or gets warped over time, workshops recommend that you have the disc surface machined or skimmed to remove imperfections and unevenness. There is nothing wrong in doing so and it is, of course, the cheaper alternative to replacing with new discs.
The problem is when the symptoms appear again after prolonged use, you might end up with another mechanic or workshop with no record of what was previously done. Skimming the second or third time will ultimately lead to disc thickness below the allowable limit. During braking, the brake piston will then need to slide out further than normal, leading to the piston "rocking" as the brake pressure is applied.
At this stage, the only remedy is to replace the brake discs. And do it immediately, before your brake pistons get damaged.