NavList:

Inside there are all sorts of things that can cause enough interference to cause reception to be lousy.  LED lights often cause interference, as well as things like phone chargers, etc.  Going outside should help in most cases and certainly try both 10 MHz and 15 MHz, and maybe even 5 MHz in the evening.  If there isn't an external antenna connector on the radio, try clipping a long length of wire to the radio's antenna.  WWV is usually reasonably easy to receive, so I suspect some interference.

Gerhard