It all depends on your actual build and what you are hitting.
If you replace another building by a tower, be prepared to get a noticeable plunder drop. Basically it will amount to 1/buildings times your plunder. At least 500k plunder loss on haunting (ally bonus plunder loss).
If you build a tower onto a new, free land, you'll observe a small drop in plunder.
How do osw's normally get started? Is it just something mutually agreed upon or does it begin with an argument or is it just my clans better than yours?
Most of them start with someone mouthing off about another clan, ally hires, excessive hits, etc. When somebody says it was for no reason, they are full of it. There's always a reason.