Many factors, every application is different. But I've heard that people with common names are taking the longest because they usually match the name of delinquents already marked in the fbi records. You can call and ask what's going on.
I filed on the 15th, app received on the 17th, Bios on the 13th and nothing here either...no worries, if you have not received a ding, it will eventually arrive...believe me, I know exactly what you are going through...
That really sucks....maybe you should call...I have the EXACT timeline like you. Sent mine in on August 15th, got my bios on Sept 17th and got approved October 9th. I strongly recommend you call....