ok i found the solution
the prev owner must have been into the habbit of screwing the
locking nuts too tight and the string had basically cut a channel into the nut making that 1 string sit lower than the rest (unless that happens through normal wear and tear anyway ? )
i changed to a set of 10s to check and tadaaa problem vanished
so i guess its off shopping for a new nut or stick with 10s
thx for suggestions / help