about clocksource in 2408 and Nuendo

[Sameti]

Hi folks:)
I have a problem that really bugs me. I really hope some souls out there could spear some minutes helping me. Please.
I use mackie d8b mixer, Nuendo, 2408 the older version, not mk3/pci 324, mac osx panther.
Ive been told to use adat a as clocksource( i use adat a, b and c) from 2408 to my mixer, opened all my 24 out channels. in nuendo use adat a, and in 2408 also, but in nuendo it automaticly goes back to internal and i get this annoying sound every 5‘th second. If i use internal in 2408 as well it get worse.. What to do??? ive just started my studio as a firm and i have this assum pressure to have it all working so i can work with my customers, but how can i theese days when i get this annoying sound now and then. i cant record properly:-(
Im trying to get money for buying external clock, wordclock and i think i choose nanosync, but until then, what to do??
Im that person that always help others, but i dont get much support my self. im really frustrated. I would really be thankfull if anyone can reply my Topic in this forum...
Please help me... Dont know what to do.. as ive written. i have the older 2408, not 3208mk and i dont find anything about this one at motu.com.. i use much money on microphones and other stuff i need, and to upgrade my 2408 would be hard when i dont have money for it right now.. but do i have to upgrade? is that the solution. when i buy nanosync i dont have to upgrade? Please help me if u know the answer! im in a real pressure cause i have to get my studio working fast as possible...

im new here, but ive used motu for many years... bought the midiexpress and 2408...

i used os 9.2 but now ive just went over to osx panther, and nuendo and thats when this bug happened..

Waiting for answers, and really thankfull if anyone reply to my questions...

Best wishes from norway:)