Thump at around 3400 RPM???

[ody]

Anyone, i was test driving a 2003 Boxster from the dealer (5k miles on it) and i accellerated semi-hard, as i was going through 3k 3.5k RPM i heard a thump coming from the backend like if someone kicked the car, i didnt notice any surge in the car, like if it hit a "power band surge"??? At first i thought i hit a pothole or something but it happened again when i turned a corner. this time out of first gear. seemed to be around 3.4k RPM??? anyone ever notice this in a boxster?? - this is the first time i have driven one (newbie)!