Do you play it or are you just trying it, experimenting?
It's only got three valves so you can play a lot of notes with the same fingering. Speed of air determines pitch. If you firm or loosen the lips, you'll get different pitches. Rattling? That could be the vavles. Something loose. Maybe a spring inside the valve casing -- They push the valves back up. Just open up of the vavles and check.Or... haha.. Maybe the valve caps are just loose. If you get a clicking when you push the valves down, they're loose. Check that the valves are positioned the right way. Sometimes rotating them will do it. Or you can check on the inside and see if they have numbers (numbers face you as you play usually) or little plastic pieces. It should be kind of obvious if the valves are in wrong. It won't let air/sound through if they're in the wrong way.Other that, this isn't the place for brass advice. Firm embouchure, good air support, etc.
But I'm really wondering... Why are or is anyone playing Eb tenor horn? Are you in England? British brass band maybe?
Practice. Have a teacher. Do a daily routine. Ensemble instruments use different skills than piano.
See if you can have one instrument at school and one at home.
maybe its broken
For air support make sure you're leading with the abs. Abs move first for sucking in air. Abs moves first for pushing out air. Chest breathing won't work well. Low brass uses a lot of air. I'm sure you know that though.