Welcome to the Frog Forum!
Ah, the Pacific Chorus frog (Pseudacris Regilla) is one of my favorite species of frogs . They're adorable, easy to keep, have very beautiful colorations, and quite interesting personalities.
As for your question, I've never had one show of aggression between my two Males, Levi and Thermidor, so I'm pretty sure, as long as enough space is provided and they each have their own little hide-out, that they'll be fine living with each other.
As for space, I'd say a 5 Gallon minimum, but preferably a 10-15-20 Gallon High tank.
To answer both your third question and your concern, Pacific Chorus frogs only frequently call during their breeding season, which I believe can range from early Spring to early Summer. For the rest of the year they'll only occasionally make quiet chirps, like you've described. I know, because that's exactly how it is with my Pacific Chorus frogs, currently.
One thing I do really want to warn you on is to make sure the lid for their tank is secure. These frogs are master escape artists, and if they escape it typically doesn't end well. I lost my beautifully colored male, Chrome, in this way.
Just for fun, here's some photos of my Pacific Chorus frogs:
A nice shot of one of Levi.
Here's a good photo of Thermidor, sitting at the top of the fake vines, his throat puffed out a bit.
A photo of my beloved, beautifully colored male Chrome sitting in the same spot as Thermidor is in the last photo. (RIP)
A quick photo of Levi and Thermidor together. I apoligize for the blurry-ness of the photo, I'm notorious for taking blurry and unclear shots! Also, as Thermidor grew (I got him as a froglet) his coloration changed. Right now, he is is a khaky color, whilst in this photo he is a light green.