H1b BG check after petition approval

Hi I work for Infy…have around 12 yrs of experience. My h1b petition got approved on Jan 16 2017.I can see a mail from hr asking me to initiate a third party back ground check related to h1b process. My first question is this check is initiated from USCIS or it is something internally initiated.because it doesn’t make sense what is the need to initiate BG after my petition approval. Again my second question is my second last employment designation has given wrong in the relieving letter by the employer. I was offered a role of lead consultant but in relieving letter it was typed as associate consultant.but i got my form 16 and income tax filing to prove my employment. I m worried will it affect my visa processing. :(… Could anyone share ur thoughts on this…