The Sony TRV900 has the ability to be set to Manual Audio Gain. I would suggest that for any shooting in the future. Set it to peak about -5db or so.(posted 8950 days ago)For existing footage it sounds like the levels are set too hot in FCP. Maybe checking the audio level part of the manual would help. Otherwise that particular camera's auto gain circuit could be too hot.
Just because a camcorder has Auto Gain controlling audio doesn't mean that you couldn't get too hot audio. Usually the auto gain circuits have a slow ramp up or down so when you get a sudden level increase that it could potentially hit the clipping/distortion/noise threshold.
Auto Gain audio normally will run hotter than good manual settings. DV audio is excellent in the 16 bit mode but it won't tolerate too hot audio.
The best choice is to use good manual audio levels whenever you can. If you can't do that then it would be a good idea to have your auto gain audio circuit calibrated down if you are getting too hot audio.
Michael C