Wife came home saying the car was making a popcorn sound. Its an Altima.

It seems like its the bearings in the alternator? Thats where the sound is coming from at least. No actual battery/electrical issues yet.

Sound like a reasonable diagnosis?

Also the prices on alternators at O'Reillys and Vatozone are crazy. Amazon, Rockauto, and carports are WAY cheaper.

Anyone have issues with those sites especially as it pertains to returning the core?

Selling the car in the next 2 months with baby number 3 on the way.

Rock Auto is great. Fair prices.

The other thing to consider in pricing is the shipping costs of receiving the new alternator, and the additional shipping cost of returning the core. If it's $20 cheaper, but costs you $20 to ship the core back, you're better off getting it locally. If there's a problem and you need to get it replaced, those additional shipping costs quickly erase any savings you might have had. It may still be cheaper, just consider the full cost.

That said, I've had very good results with parts from RockAuto. I don't trust rebuilt starters from Autozone or Advanced at all.

Just sell it now

RMN25 coupon code saves 25% off at Advance Auto online for pickup in store. Makes their prices comparable to Rock Auto or Amazon.

I've quit buying parts like alternators, starters, and fuel pumps from online retailers. I've had to fight with Amazon and Rock Auto to get "lifetime" warranty items swapped out. Much easier to just walk into a retail store and get a replacement same day.