According to a growing number of user complaints, it seems that more than a few Pixel 3 and Pixel 3 XL owners are reporting that their phones are experiencing call quality and connectivity issues, in which their phone calls have audio quality problems where they sound choppy, inconsistent, and in some devices, it can sound quite “tinny”.
According to Android Police, based on the number of reports, it appears that the problem isn’t necessarily restricted to any particular model of the Pixel 3, nor does it seem to be isolated to any particular carrier either. In fact it seems to affect both WiFi and cellular calls, although some found that disabling Advanced or Enhanced carrier calling features has helped, but your mileage may vary.
Google has since issued RMA replacements for some of the units that have been affected, so you can try your luck getting a brand new unit if you’re faced with similar problems.