My cpu makes a high buzz noise when temp gets over 50c

Typically, this sort of buzzing is the result of poor grounding. It could also be a vibration issue that you think is a buzzing problem.

If you disconnect the speakers, does the problem go away?

Hmmm well - I can't say for certain what it is - but I can tell you what it might be.

I read somewhere before about some motherboards that give off a high pitch buzz noise - which apparently comes from some capacitors on the motherboard which supply your CPU and other devices with electricity. I forgot what exactly it's called though.

Do you know if the noise comes from your Motherboard, or power supply? That would help a lot.

By the way - what is your power supply?

the problem was never existed before this new mobo and cpu. the rest of the computer has been the same since my old build.
if i disconnect the little computer speaker, then the sound goes away.
i assume it is a mobo bios or some sort, but not sure exactly which part

This does not sound like coil whine. That is usually in the PSU or GPU. It could simply be an issue with the piezo speaker (the little speaker) itself. Swap that out to see if it helps.

Is it safe to assume that everything else works well? How are your system temps when the system is under load?

i am curtain that it is not my PSU since i've been using it for quite a while since my old build while it was running prime 95 as well.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

the sound came from the system speaker that i plugged in to the mobo.

according to coretemp, while web surfing, i'm at sub 20C, never exceeded mid 40C in game. however, i'm trying to do stress test with prime95, so the processor actually reach 50C but never exceed it. At ~49 the little mobo speak keep making the buzz sound on and off. the sound is off when it goes below ~49 and constantly on when it reach ~49 or higher.

Could simply be vibration caused by the fans spinning faster when the system heats up. Those little speakers often come into contact with other things (like wiring) and can certainly be annoying.

Is there a bios warning sound set for when temperatures hit 50?

good idea, but i set it to auto shut off at 90C

yeah, i've had that problem before too. but this time is not it. thanks for all your idea. i need more!

How loud is the buzz? It could be a BIOS temperature warning. Check to see if you have the CPU Warning Temperature enabled in the BIOS:

CPU Warning Temperature Sets the warning threshold for CPU temperature. When CPU temperature exceeds the threshold,
BIOS will emit warning sound. Options are: Disabled (default), 60oC/140oF, 70oC/158oF, 80oC/176oF,
90oC/194oF.

coretemp said my CPU temp is 50C and never gotten any higher even when i run prime95 for half hour. i would have keep it running, but he sound was too annoying, so i made it stop.

high buzzing noise can occure from badly fitted hsf. symptoms include increase of noise to temp...
if its a whistling noise its likely to be a cap/voltage module thats close to the cpu.
if it sounds like an earth buz.. ie low tone. then cheat the pcu placement and make sure you have no tim or hairs blocking the cpu pin sockets.

Food for thought, but possibly EMI? That could cause the speaker to buzz... Maybe reseat the motherboard and components and make sure all the standoffs and screws are in place... unlikely but worth a shot.

If anything, just unplug the bios speaker. It is not required unless you are troubleshooting anyway.

Or try what digitalzom-b suggested