What happens when the underlying samples have a high enough value that adding 16384 would push them over the top?
By the way I'd say your left channel needs a smaller amount (2000) adding every three samples as well. And I don't think the offset on the right channel is 16384 - it's more like 20000.
StainlessS: I've got this one covered if you don't want to spend any (more) time on it
Just waiting on an answer to the above question before finalising.