There seems to some regularity in the irregularity.
a – e is found for example in tann – tenner, and – ender, hand – hender, strand – strender, kraft – krefter, mann – menn, far – fedre.
o – ø is found in bok – bøker, bonde – bønder, fot – føtter, bror – brødre, mor – mødre.
e/å – æ seems to occur in words of one syllable ending in a vowel, for example tre – trær, kne – knær, tå – tær.
datter – døtre is completely irregular; the reason is that datter used to be dotter long ago (still is in Swedish).
If anybody knows about a complete list of Norwegian nouns with sound changes between singular/plural I'd be happy to hear about it.