Vibration from rear

Hello,
I have a 2003 zx2 with about 50,000 on it. Took it cross country last summer. While moving through Nevada, I tossed it into neutral as I went down a long incline. The RPMs jumped horribly, and it freaked me out, so i slapped it back into drive and continued on. While driving back to kansas through the southwest, I started to notice a hum or vibration coming from the rear of the car. It is not that load, but noticable. One mechanic said perhaps shocks/struts, but the rear tires do not show strange wear patterns. I checked the rear barrings via the lift and shake method, but the bearing seem fine. So, now I'm wondering if it could be transmission related. I have noticed that it slips a bit when I put it in park, and it once gave a couple of second lag going into gear. What do you all suggest? Is there a way to test the transmission? Could my high speed shift into neutral mess up the transmission? Does not seem logical.
Thanks for any help you can provide
quincy

Could be the tranny. The autos are notorious for problems. The revving, could be related to that. On a side note, when driving, putting an auto into neutral while driving, even on a hill, is not a good idea, because in neutral the motor revs more than in gear, as well as the fact that you may need the motor power if something happens (ie blowout). Its just a not a good idea, so when driving an auto just leave it in gear. The idea comes from manual trannys when trying to save gas, which even then puts more strain on the clutch and tranny. just a suggestion.

fwracer

you have an auto that even made it to 50k be happy, most auto trannis die 20-40k

When you put an auto (especially a transaxle) in nuetral at high speed, you are turning the wheels and differential at high speed without the benefit of the high volume oiling and cooling the the tranny produces for it when engaged in gear.

My guess, you overheated the diff. Probably find a bunch of heat-blued parts in there. Doesn't always mean it's shot, I've seen them run for years and years with howling or whining gearsets.

I wouldn't worry unless it suddenly gets worse.

Thanks for your imput!

Had the same problem with a manual tranny. I shifted into netural going down a hill and forgot to put it back into gear when starting back up and revved the (you know what) out of the engine. The engine vibrated terribly for the next 20 miles. Slowly it came back and did all right. I'm lucky I didn't throw a rod or spin a bearing.