Why?? [280x]

I have a Sapphire R9 380 and yesterday I got an Asus R9 280x. I know it's old but I got it for $ 80. However, I'm only getting 13Mh / s in Claymore. I'm setting 1500 memory / 1000 core clock with afterburner and I get the same if I set 1300/1000, etc. I do not know why I'm only getting 13Mh / s. Reading posts, I've read that other mates have better performance ( https://forum.ethereum.org/discussion/3940/23-mh-s-for-a-r9-280x ). With this hashrate it's still profitable for me, but I would like to know why I'm getting only 13Mh/s... Has anyone any idea? Maybe an issue with the drivers? What drivers should I install? should i use another mining software?
Also the f***** fans are running at 100% although I set 50~70% in afterburner, sapphire trixx, Asus GPU Tweak...

Thank you for your time.