how can you tell if wheel bearings have gone bad, back wheels make all kinds of noise when I hit a bump no noise on a smooth street or highway

 

Then thats not bearings. Bearings would make noise when moving. What kind of noise is it? What year Caravan? How many miles? Start with a thorough suspension inspection.

 

As jkeaton said, not bearings. A few details would help diagnose the problem.

 

2009 caravan front suspension was done over new shocks in rear, noise sound like a rattle, sometimes it sounds loose pieces of metal

 

It chould be pad slap but I doupt on rear. I have rattle sounds like from rear but I think my dealer said side door adjustment.

 

We live on a gravel road and we have the same problems with our rear wheels.
You can really hear it when you back up, screams, screeches, it sounds just like metal scraping, sometimes after backing up and driving forward you can hear it, it is just awful.
My wife complains about it all the time and I keep telling her there is nothing I can do about it, but she don't believe me so the next time I was taking the brakes apart for quarterly maintenance I made sure she was there to see, and when I took the rotor off 4 - 5 small and bigger rocks fell out, that is where your problems most likely is, rocks gets on the inside and scrapes the rotor and the parking brake!!!
Sometimes it sounds so bad that you would think that the rear end is coming apart, it makes you think that you are going to flip forward and the rear end falling off while your flipping.
If your side doors are loose and they squeaks, you can tell the difference because the noise is right behind you, not at your rear end which is further back.

 

'08 - up Caravans have crappy rear calipers, as the parking brake is prone to hanging. I was on the way to get new tires in the rain the other day, and heard 'em squealing.

Took it back to Monro Muffler, where my buddy did the new brake pads about this time last year. Pads front and rear look GREAT... rear calipers are SHOT where the parking brake has been hanging.

He got it "unstuck," so it'll pass state inspection. Tax refund in the spring will go towards new calipers. And we can't use the e-brake UNTIL then...