I wonder if bandit attacks will be random where they could happen while your away on a quest or if they only attack when your at the settlement. The whole bandit attack thing could in theory turn into a mini game where your constantly travelling from settlement to settlement doing repairs and upgrading or changing the layout of your defences to try and make them harder for bandits to attack while protecting your settlements. What's your thoughts on this?

I suspect they are going to constantly happen, whether you are there or not, the size of the attack groups and the frequency most likely connected to the size, the bigger and more prosperous a settlement is, the more important it is to set up npc guards and turrets, otherwise bandit attacks become busywork.

As far as we know until now, they are likely to happen randomly.

Although I still hope that settlement proximity to danger zones e.g. raider dens, deathclaw nest will affect the frequency of attacks on settlements...

I think they will happen while you're gone too, but the outcome depends on the number of defenses and weapons you got.

I would like to know if we will finally see some attacks on normal settlements. Everywhere are Raiders, but we never actually see them "raid" anything...