If the mount is rigid, and it isn't the shooter...it's gotta be the scope...
Given that it's a $75 optic, that's probably a safe bet.
You should consider spending more to get something reliable. What if you were on a hunt and it failed?
Far as "tapping" on the scope...sure, have at it...but it isn't going to fix it since it's broken...
They pound Nightforces on the table (HARD) as part of QC.