Found several threads discussing similar issue, but nothing exact same.

This started happening today - I can feel a periodic rumbling vibration(every second or so).
Onece every 4-5 such vibration causes the whole car to shudder (can see the car shaking
if paying attention). No CEL so far and seems to drive normal. This is more pronounced while
at the signal and such.

Coil pack? The dealer said my car is not affected by that recall. And ideas appreciated.
Yet to pull codes.

Just when I was all set to go on vacation, oh well... I'd hate to rent for the holidays.
And was at the dealer only last month for another issue, gosh hate to go again...

 

Forgot, it is a 2007 A4 (58K miles)

 

It may be a red herring, but when my Mustang started doing this, it took about a day or two to throw a code and turned out to be an O2 sensor. Odd thing is that it smoothed out once the code came up--maybe the ECU started compensating once it knew that sensor was offline. If that's it, though, probably no way to know until the code pops.

 

Actually my O2 sensor did go bad, at as early as 5K miles. Just got a CEL at that time, no shaking like this though. Will update what I find out ...

 

So it was at the dealer for 2 days - they replaced the crank case breather valve and turbo pipe. They also replaced the intake manifold and fuel pressure sensor, which I suspect was more of a precaution.

All covered under the extended warranty, didn't pay a dime. Thanks to Audi, saved me a ton. Surprising I was driving around for a week, with no CEL or any noticeable difference in the drivability.