My diagnoses
X2 on the starter not being bolted down completely.Front brace missing...?
Starter nose deformed from front brace missing and bolt falling out.
Thanks for the video,makes the diagnoses easier.
Remove the starter and check the nosecone for cracks and deformed holes.
Get new GM starter bolts and front brace.
Install and re torque the starter bolts at each oil change.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews