The two Red pups we had. I don't recall ever hearing them bark? But they would make an "acking" noise. As their fur was hackled up & they moved about stiff-legged. In an agressive/defensive? posture.
As for the "yapping" & other noises. I suspect that yapping was to call their parents? Pups were around 10 wks old or so.
Some yrs back, an old friend & I. Sat in my truck next to an active Red den in a high cut road ditch bank. Waiting to get some pics. We sat there until Sunset & awhile later.
Two pups eventually came out to look around & play near the entrance hole. After 10 minutes or so, suddenly two coarse short loud barks. Came from within the den hole. Et those pups instantly stopped what they were doing & shot down the hole. They never came out after that. We moved on.
Interestingly, those two den site pups never made a sound in our presense. I suspect, because they were secure? & one of their parents was inside of the nearby den hole.