The sound seemed like it might be coming from the alternator (it's
really hard to tell) and since it's the only small diameter pulley in
the system, it seemed logical that it would be more prone to make noise
with the cross-grooved Dayco belt. The tension seemed OK, but I
tightened it more just in case. It now deflects ~1/8" with
light-moderate pressure.

One more question. During reassembly, I managed to leave out the lower
timing cover bolt that's behind and below the water pump pulley flange
(the hole wasn't visible and I missed it). The cover seems secure and
there's no way I can get the bolt in there without some significant
disassembly. Is there any compelling reason to go through the hassle of
replacing it other than pride of workmanship? It bugs me to have made a
mistake, but I can live with it as long as it's not going to cause a
problem.