Is something wrong with my new cockatiel?

I just bought a cockatiel today, i got him because he was really joyful and was always singing and was special from the rest, he seemed quite social. When i brought him home he loved the mirror and was always singing VERY loudly and still is, he has tunes and sometimes quiets down, he keeps fluffing up for like 2 seconds and then shaking (like a dog trying to get dry) but the weirdest thing hes done is he keeps pecking the sandperch (like a woodpecker) and keeps hissing at nothing. He has a normal sized cage with enough room to run around, he has a calcium thingy, a mirror with beads, lots of water and food, 2 sand perches and a wood, and two dangly toys with bells. Is something wrong with him? I havent touched him because i know they need like 4 days to adapt, but how can i make him more comfortable, is he sick?