On final, with one notch of flaps, 90 kts.,
descending heard what I call a rattle. From the left seat, it sounded as
though it was above to the right. PAX heard it in front of him. I think
it’s some interior trim or molding whose Velcro has come off and when wind and
pressure hit it rattles for about 10-15 seconds then goes away. No impact
on flight controls or instruments. PAX watched all the gauges while I
tested all the controls. We turned AP on and off. Switched COMM from 1 to
2 and anything else we could to isolate it. Doesn’t appear to be any
immediate safety problem. Anybody else have similar experience.
I have had something similar. It almost sounds like a seat belt is hanging out the door and slapping the side of the plane?
Tom,
I had a vibration come and go in mild turbulence and more often on approaches…to final…make sure your exhaust pipes are secure especially regarding vertical movement. If the springs get worn or the bolts securing the pipe to the exhaust brak or become loose, the pipe will easily move up and contact the its shield on the belly and give you a pretty good vibration/rumble.
If you have the door key lock in the locked position without the outside door handle engaged by the lock the handle will (under certain conditions) rattle.
I am not saying I did and I am not saying I didn’t!!! 
Next time you have the upper cowl off, check the air baffles on the right side and right front. I had the same noise, always when on decent at or near idle power. My engine baffling on the right side was cracked over about 20 inches, from the front lower corner to the middle of the upper right side. I just had it replaced last week (along with a broken left side exhaust pipe), and the noise has disappeared completely.
I have just developed a wobble ( new term for the web site ) when pulling the power back from takeoff / climb rpm 2700 to 2500 cruise a wobble style vibration starts to shake the instrument panel. I think I may need my prop balanced. Someone quoted $450 for this job. Is that about right?
This could be a loose wing root fairing. The OurPLANE SR20 had one and the sound fit your description.
We had our SR20 prop balanced for $160.
my pilot side fairing needs new double sided tape, maybe that is the problem
I highly recommend balancing the prop. On my own plane the difference was quite noticeable and the resulting smoothness well worth the cost (never mind the decreased stress on the engine and its mounts, etc.).
I would of thought the prop came balanced? N76D
The propellers that come from the Hartzell factory are statically balanced. The propeller after installation should be dynamically balanced with a Chadwick or equivalent method to about 0.5 IPS or less. The cost for this service is typically 3 hours shop labor for a single engine aircraft.