It's important for everyone to remember, there is still raw-material variation and tolerance stacking even with quality tools/suppliers/and work. In the modern world, we don't always see the industry equibliriate with a process that QCs to a 0.00% failure rate, its more economical to have 98 or 99 or 99.9 % etc standard (ie "good enough"), which means occasionally you will need to warranty a part or a service. This seem to be true even with higher-grade brands and product grades.