Here is my 2 cents. About a year ago this time I experienced problems with a double buzz. I found that I was continually playing fatigued. In other words I was not allowing for enough time during my routine for rest. I adjusted my practice to include other musical activities such as sight singing, listening, and score study. I essentially broke up periods the periods of high intensity trumpet work to ensure that I remained fresh. In a matter of a few weeks the problem went away and has not returned. Brian Goff also has a discussion on the topic on the website that you might find useful.
http://mailer.fsu.edu/~bgoff/tpt-tips/tip107.htm