Elantra belt change question for Hyundaitech

It certainly doesn't sound like a problem. If it persists, you might want to doublecheck the alternator belt. In most cases, even experienced technicians, if they're unfamiliar with Hyundai, leave the alternator belt a little too loose. There should be nearly no deflection in the alternator belt with light pressure. The A/C and power steering belts don't need to be quite as tight.

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.

It's possible the cover could bow out over time and contact the water pump pulley. Then again, maybe not. You've basically got the four corners tacked down. Worst case scenario is probably that you need to replace the lower cover the next time you do the belt.