Just filed N-400 online earlier today.
Haven't received an NOA yet.
I also sent a packet a little under two weeks ago to amend my existing I-751 joint case filed 13 months ago, adding a Battery/Extreme Cruelty waiver (428 pages).
I haven't been notified of anything on the amendment of my I-751 yet, so I imagine I might not receive my N-400 NOA before they check that my I-751 amendment request is duly registered.