New cello sounds metallic?

I had a 3/4 sized student grade cello. It was too small so I got a full sized. It is an intermediate level and I'm getting used to a bigger instrument but the A and D strings sound metallic. The D string metallic sound is bearable when I put more weight in my bow but is noticeable (to me). But no matter what, my A string sounds really metallic. My open A sounds hideous. So does open D. When I start bowing on the open A it sounds like out of tune G sharp that after a second or two decides to become an A. This only happens when bowing. When plucking everything is in perfect tune. What is happening? What can I do? The other strings are fine. The cello has been used for a year by two people and should be okay. Is there anything I can do?