I did the check level and I say's the volume is OK. That volume is OK and reads 75 db on my digital radio shack meter. Them I go to do a measurement the volume in much louder then when I calibrate it or do a check level. I have to lower the volume on my PC from when I set the calibation so it's not so loud and displays it in the correct range.
I had the same problem when I was first sing REW. I have RS meter and Galaxy, and ECM 8000. I played with the program enough until it just did not do it anymore. I could not tell you why the volume was so tremendously loud on the sweeps, but it would almost tear my house apart and I could not figure ot how to stop it. It does not do it anymore, but I cannot tell you why.