One reason for not using old spokes and nipples is it exacerbates spoke twist as the threads are not so clean in either. But, it really depends how they look.
If they go on ok and you give the threads a light oil (along with the eyelet all should be good). Only other problem is knowing how they have been treated before!
If you hearing metallic pings and you ride a new pair of wheels down the road, its probably due to the spokes not being relived during the build. Spoke twist builds up as you tighten them and if not oiled/ relieved enough the heads " ping" as the weight on the wheel temporally reduces the tightness if the spoke in the hole.
If youve done you build right.....it should not happen.
If they go on ok and you give the threads a light oil (along with the eyelet all should be good). Only other problem is knowing how they have been treated before!
If you hearing metallic pings and you ride a new pair of wheels down the road, its probably due to the spokes not being relived during the build. Spoke twist builds up as you tighten them and if not oiled/ relieved enough the heads " ping" as the weight on the wheel temporally reduces the tightness if the spoke in the hole.
If youve done you build right.....it should not happen.