Can someone tell me where I am going wrong!!

When I join a 3 file avi rip with virtualdub or nandub the 3rd file screws up my audio. I can join 2 files no problem It's only when I join the 3rd that it goes wrong.

I've tried joining 2 and then adding the 3rd and tried joining them all at once.

Any help would be appreciated

Thanks in advance.