drive train thump

hi all, let me start by telling you about my truck. this is my first tacoma and have to say i love it. its a 08 reg. cab 4cyl 5spd i got it used 33000 miles and no warranty. my problem is when i brake at 40mph+ i get a strange thump,thump,thump from somewhere in the drive train. i have a habit of pressing clutch + brake together, so i found that if i just brake no thump but as soon as i press the clutch thump,thump,thump. i have done searches and havent found any of them with the same problem. if anyone has an idea of what this might be it would be very helpful. thankls

 

wow this is hard to belive. with the knowledge on this forum and no answers it sounds like i might be stuck with this problem. i will post the cause of this if i figure it out. thanks.