screen "spinning"

I think it's normal. I have used both Garmin C340 and Nuvi 350 and noticed the same on both units.
Maybe it is because the relative distance between earth and GPS satellites are never constant and the units registers the change...
Just my $0.02

If satellite reception is not great, the changing strength causes the unit to constantly be fine tuning your location. If you are moving, you don't see it, but if you are stopped, the changing position is interpreted as vehicle motion. If you have it in 3D or Track Up, it will spin the screen.

200w - the same problem with rotation on my unit
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Is the world still spinning around I don't feel like coming down

i have a c330 and never had that problem . maybe contact garmin and see if they have had other units that have done this.

The next time you see that, check your satellite reception. You'll probably see that your reception is not very good.

While sitting at a stop light in a deep canyon in downtown Chicago, my Nuvi 350 did the same thing. Even worse, it jumped forward 2 blocks, recalculated and told me to turn. Then a few seconds later recalculated and put me back where I was.

Thanks for the info everyone. My reception was hit and miss all day yesterday due to storms. Seems to be working fine today.

When I am backing out of parking space at a mall the screen "spins" thinking I have instanstaneously reversed my direction and slowly reorients the screen to reflect the new course. When I put it in drive, same thing happens. to reorient the correct direction of travel.

My guess is that while you are sitting still, the accuracy of the reception is changing and as it does that, the unit thinks you are moving so it flips the map to match the direction it thinks you are going.

It has happened to me a few times also.

Mine will do the same sometimes when I am still. It's probably a little like me, I can't sit still either. But it works great when I move

Yes, I agree with the above, it is because your unit is recalculating its position and altitude because you signal strength is not great. It does it on mine as well.