Unusual Trend in Amazon Marketplace Sales

We've been selling our products on Amazon for about 3 or 4 months now and I've begun to notice a pattern with the sales. It seems like we get 3 or 4 good weeks of sales, followed up by 2 or 3 weeks of slower sales. I'm highlighting this trend with a graph of our sales over the past month (numbers obscured, just showing the concept).

You can clearly see the rise, the steady sales, the drop, the rise again, then the last dip. Over the past weekend, sales have really shot up once again and we'll probably do record sales over the weekend for our items on Amazon (thanks customers!).

I've been trying to pin down the reason(s) for this. At first, I thought it might be feedback related; but our feedback was trending very positive (about 92% positive) before the latest dip, which was about 2-5% higher than before and we also have more products in stock than earlier in the season. So that's not the cause.

We've also been updating UPC codes for our products, so they relate better with current product on Amazon. Sales did not rise or fall after starting to include those to our feeds, so that is not the cause either. On this note though, we've noticed that bigger companies (Target, for example) are using the improper UPC codes on some products which causes problems. Since they are the "authority" for some products, their information supercedes our own. This has caused a few problems over the past week, where Target claims a given product is 72 inches long, when it's actually 36 inches. Target uploaded the product as 72 inches, using the 36 inch UPC code. Nice, Right?

I'm guessing that Amazon somehow cycles the sellers around, to make sure everyone gets their products listed well on average, instead of having a few people always appear on top. This makes quite a bit of sense; showing different results all the time would help customer retention.

Either way, the ups and downs are very confusing. We are just hoping that the cycle is up during the busy Christmas shopping season.