There is a thing, which drives me crazy.

I used 2 camcorders, which split after 4GB (about 23min, 1920x1080p 50fps). Then I added 2 files of the 1st camcorder in a video track, and 2 files of the 2nd camcorder in the 2nd video track. Both audio tracks are activated and it sounds very good. When I add the 3rd video file (automatic split at 4GB) it gets crazy. There is a lot of echo. After an automatic audio alignment there is a difference of 8 frames, same when I try to align it manually. I cannot hear the audio uninterrupted, with full zoom, probably the single frames take too long to read from the harddisk, but with a little less zoom the echo is gone and everything seems to be fine. I save it, load again and listen to it with nearly no zoom, and there is a lot of echo, seems to be that I have to move -2 frames (in the other direction). It looks like the echo depends on the zoom level or it is a random effect, if I here an echo or not.

Any ideas?