Hi,
"I'm sorry if I had disturbed you the other day"
vs.
"I'm sorry if I disturbed you the other day"
Could someone make up a sentence where the use of "had disturbed you" would make sense?
You told me to be quiet. I disturbed you. Here, it sounds like the disturbing came after the telling.
You told me to be quiet. I had disturbed you. Here, the disturbing clearly came before the telling.
You need a context that involves two different points in the past. You can then use Past Perfect as a means of clarifying the time sequence. In your two examples, you don't have a context with two points in the past.
Best wishes, Clive