It's very easy to mishear where a noise comes from in a PC. I had a smilar issue with my "monster". I thought it was a fan and actually it was the MB tray that was not well tightened and vibrated.
It's technically possible to replace the fans and/or cooler on a graphic card but you really need to know what you're doing. It's more complicated than for a CPU.
I don't know how much you want to invest. Currently, with the games we play, Nvidia works more safely than ATI (but many ATI cards work just fine, only some have issues; it's a pity as, in low and mid-range, ATI is usually a bit better than Nvidia for the same price). If you go for Nvidia then have a look at what Asus makes. They have good series. They are not alone of course.
500 series
http://www.newegg.com/Product/ProductLi ... ageSize=20
GT series (including "low" so-called 500's which are not really 500's)
http://www.newegg.com/Product/ProductLi ... ageSize=20
But they have no GT 450 listed
For all-purpose and a good upgrade over your 230, I'd say try a GT440-based card.
ASUS ENGT440/DI/1GD5 GeForce GT 440 at "$94.99 $74.99 with Rebate"
For better gaming, go for a GTS450 as it's not a lot more expensive and it offers 70% better performance in many games...
None at Newegg but probably because they price the GT550 very close to the usual 450's price. Can be easily found elsewhere though.
If you want to invest, a GT550 is just fine for any game. No need to invest in a 570 like I did, it's a bit extreme.
The ASUS GeForce GTX 550 Ti (Fermi) ENGTX550 TI DC TOP/DI/1GD5 Video Card at "$139.99 $119.99 with Rebate" is very nice.
For what benchmarks are worth, you can find some there (among many others):
http://www.tomshardware.com/charts/grap ... rds,1.html
Note: most Asus cards have a specific cooling system working well but taking room. You often need to have the slot near your video card's slot free.