dell xps 8900 desk top

called dell support today to ask about a knocking noise when i start computer ,so he ran some hardware tests and every thing seems OK,so then he checked the registry and there was whole bunch errors ,he said that the warranty does not cover software issues ,this computer is a refurbished unit about 4 mo. old,he proceeded to tell me it would cost $150 to fix this ,The computer seems to run good,so i refused to accept this,running win 10 latest edition ,he was kind of pushing me to spend the money to fix this"problem".I always thought that the warranty covered everything,computer is running great ,why fix something thats not-broke.i have been buying dell for the last 20 yrs. this will be my last dell!!!!!!