We have a customer that is sending back product at a high rate of return (10%) reporting problems such that screws won't screw in. After looking at a couple RMAs as well as stock, mechanical engineering has determine there is no problem. More specifically these tapped holes are pretty small (4-40), and in inspecting stock the feedback was 5-6% of units in stock (different distribution but in the right ballpark as rate of return) won't screw in the first time, you hit a stopping point but after backing the screw out and trying again on the second or third attempt the screw goes in without issue. This seems odd to me and I can understand why the customer is sending back product, but I'm also not knowledgeable in this area. I've registered the customer complaint as an issue in our system and once we hear back from the customer we will close the issue out. Although, the explanation doesn't sound right to me I don't think there is anything further for me (quality manager) to do as both engineering management as well as sales manager (same person) is in agreement there is no issue. Is my thinking correct - close it out and move on?