I drive a 2007 350Z Enthusiast. Recently I have noticed when I go higher than 2nd gear, usually 30 mph, I get this loud, car shaking, thumping noise. It vibrates the whole cab and feels like I am going over a series of small bumps. It has only happened twice in the last two weeks, so I'm not too worried about it, but I was wondering has this happened to any of you guys? Thanks in advance.

 

My first guess would be a rear diff bushing on the way out.

But you need to be more specific...

Does it occur only under acceleration or does it also happen while steady state cruising? And similarly, when you shift or when the car is just moving while in gear?

Is it localized to the front or rear?

How are your tires?

How many miles on the car?

Stock suspension?

 

Since it's only happened twice in 2 weeks, I have a different guess. Maybe a failing driveshaft u-joint that occasionally binds one or more of its bearing caps. Happened like that in one of my Alfa's and quickly got progressively worse. Just a guess, though, and considering Mic's questions will lead you in the right direction.