I snapped one CV axle bolt before in Nascar318is's car and with just one bolt gone on one axle it had a very noticable shake. If some backed out on you I'd think you would have noticed before it did that kind of dmg (I also think very unlikly a loose CV could do that).
Even if the diff was mouted loosly it would have the tendacy to feel like the car is taking off before it actualy is.. probably with some banging noise in the back too, search "front diff bolt snapped" none of theis guys had that happen even with just 2 back bolts holding it in.
Neither suggestions IMO wouild cause that.
My first geuss would be a small crack already their before your install. Dropped in shipping most likly and you just never noticed till now.
My 2 cents.
"They say ignorance is bliss..... I don't know what the Fu*k that means but I'm pretty happy". Ricky Trailer Park Boys.
Current Mods....X-Brace, Stromung Cat Back Exhaust, 17/225/45 M3 Replicas, HotBits Adjustable Coil Overs, 40% LSD 3:91 Diff, E30 Gearbox, Boosted.