knocking while driving!

help!! 2007 cobalt, 4cyl, 5sp manual tranny, 82k miles...

when the car is moving there is a defined and loud knocking that's almost a humming noise. sounds like it is coming from the tranny, idk. it is not the engine, there is no knock unless the vehicle is moving. it varies with the speed of the car, and is really noticeable once it hits like 25mph and up. you can feel it a little in the car and steering wheel, but mostly just hear it. if i drop it into neutral while moving it still knockshums until the car comes to a complete stop. once stopped no knock/hum, even if revving the engine. i've pulled off the wheels and ran it, still noisy, pulled off calipers and rotors, less noise but still there. when i stop the drivers side shaft while it is in gear still knock but not so much. when i stop the passenger side shaft the knock is louder and more pronounced. i've searched the interneet for two days to try to find what's wrong here. i pulled off the drivers side cv shaft and it seems fine. maybe a small hitch in the bearings, but idk. however when i ran it with that shaft out and the other still in i did not hear the knocking. i know it was not under load, but is it the cv shaft maybe? the inner joint? would that knock? please help, thanks in advance for any suggestions....

btw, with the cv shaft out, i can clearly tell that the wheel bearing inside the hub is bad. i've had bad bearings before but can it get this bad and be so loud? this is the woman's car and she doesnt do a very good job of telling me when something is wrong until it is too late. i drive it from time to time and check it over. this has been sounding this way for approx 2wks, she was just chalking it up to tire/road noise...obviously it is not, swampers wouldn't make this much noise! can it really be the wheel bearing??

The best was to check this is with the tires on and the front end off the ground. Place your hand on the top and bottom of the tire and pull out and push in opposite of each other. If the rims move or give then the bearings are bad. And yes they can get that bad. This is a very easy fix though. Just take of the wheel, caliper and bracket, axle nut and then the three bolts that hold the hub on. Should take about 30 mins for one side. I would do that seeing as it is cheaper than a trans. Though if it is an O7 and less than 100k miles on it, the power train is under warranty.

well, it was the wheel bearing. parts store wanted $180 each for the bearings...for $45 each i got a whole new wheel hub assembly (with hardened lugs, non-stripped) on ebay. well worth it! (seller was 'detroitaxle' and they had very good customer service, pointed me to exactly the part i needed)

i have to admit i was surprised that a bad bearing would make that much noise, i've never had one that loud.

thanks for the advice dorfboy. on a side note, i did try all that wheel moving stuff before and the wheel did not move at all when grabbing the top and bottom, that is partly why i questioned it being a wheel bearing. i've never had a bad bearing that didnt wiggle. oh well...

on a side note- this does not seem to be a very lively forum does it? i guess cobalts dont break ;-)

You are right. They don't seem to break. I had my 2007 from new to 91,000 miles (before I totalled it) and I never even had a chance to change the brakes. Oil changes and a couple of air filters. That was it. Great cars. Mine still felt, drove and sounded like brand new. I suppose the board will perk up a bit as more of them reach the 150,000 mile range.

Cobalts do break. I have an 06 LS and it has been a NIGHTMARE, with my first problem starting 2 months after I bought the car brand new :banghead:. I will NEVER EVER buy another Cobalt or Chevy for that matter. I am getting my car fixed and trading it in on a Honda. I am not sure why I let my husband talk me into getting this car in the first place...

If we have the experience in driving and a vehicle repairing,it would be easy for you to find the knocking sound but sometimes it won't be caught and might blaming us as when you speeding vehicle,the sounding occurs otherwise not.