Couple of weeks ago I noticed a noise in the speakers. At first I thought it was caused by some vibrations of the dash board. The noise actually follows the RPM of the engine. It is like a wining that increases in volume when I accelerate and I can hear it even when the stereo is off. No upgrades on the stereo system. Can it be something related with the alternator?
Thanks

Yes, whining noises are usually charging system related. If the alternator has a faulty diode, it will whine, if the battery is weak, the alternator will whine. If the static suppressor inside the alternator is faulty, it will whine. If the alternator is overcharging, it will whine. They sell alternator whine suppressors at stereo shops but put off buying one till the alt. battery are diagnosed.

Thank you carnut, I will have them checked

Well, besides the whining noise in the speakers, I've noticed that once in a while, mostly when I hit the break (but not always) the voltage goes down and it looks like for a sec the power is down, the door lock clicks like when I start the car - everything happens in one second, therefore the car doesn't stop running.
Is there a contact I could check or what can it be? I hope the alternator is not dying.
Any suggestions? Thank you!

I forgot to mention, I got new codes RFA B3108 Current
IRC B1982 History
IRC B1983 History At some point the IRC's codes were Current

Simply have the alternator checked. Not just voltage output but amperage under load. voltage is not the primary reading you want but what amperage the alternator can produce under load. If its rated at 100 amps, then put under a load, it should provide close to 100 amps. I never put much stock in history codes. Erase them and see what returns as current.