Turbulance in Detroit?

I recently flew from Detroit to Hartford, CT. The plane seemed to hit quite a lot of turbulance - the flight attendants were seated the entire flight. After reviewing several days logs of NW 1184 it seems that this happens quite often. The flight I was on was flying at 39000 4 minutes after takeoff and a minute later had dropped to 10000. Other flights seem to take longer to get to the higher altitudes and don’t have a drop like that. Why would this happen? Personally, I did qet quite scared.

Radar glitch. Mention many times before. If you really were at FL390 4 min after takeoff, that would be approx. 9,000’ per min climb. Don’t really see that happening. Also, a 29k drop in altitude in one minute would probably rip the wings off most commercial aircraft, not to mention, anything not strapped down would be either suspended in mid-air, making it appear to float in the cabin, or would slam up to the ceiling of the cabin, then come crashing back down. Simple logic would tell you there was some sort of glitch in the reporting FROM THE FAA (notice, it is not FA).