Pela idade, o barulho pode ser o cooler do processador. Talvez uma limpeza resolva, mas só se você se sentir a vontade para abri-lo sem danificar. Sobre a pergunta: Uso muitas abas do chrome aberto, será que seria só isso para deixar o macbook devagar ? Sim. Usa o Safari que vai sentir a diferença.
It happened to me after I replaced a screen. I totally agree with iwillfix. A lot of people say you must turn brightness/auto-bright off/on, wait a little, sing a song, yadda yadda, but if you just wait you're good to go.
hello! try replacing the phones. a bit of rust or dust in the jackphone could cause a noise similar to static. try cleanning it with a cotton stick, care to not leave cotton on the jackphone. you could also try playing at a base station (if you have one) to know for certain if it is not a jackphone problem.
Try connect your phone to computer and enter DFU mode. To enter DFU mode: With the phone both connected and turned off, hold your power button for 1 to 3 seconds. Then press and hold the home button without realeasing the power button and count 10 seconds. Then, release the power button and still holding home button and count 15 seconds. If you already did that and doesn't work, I would say that some board may be broken. Maybe your dock connector board...