distorted audio in export

Hello i have this weird problem, never had something similar before.  I have a video with a still image going on for all the 30 minutes , and as audio i have 4 audio tracks

these audio tracks are fine when i hear them in timeline. But when i listen the exported file, i gest a kind of distortion , always at the same point. Once it was fine, but the spoil was just moved ahead

Don't know what to do

I am exporting a custom frame size 600x450, h264, 4 mbps

audio aac,codec aac, 44100hz, stereo , 192kbps  bitrate

Wat could be the problem?

thank you