the reason your sound is staticy is likely some poor hardware in your monitor or the jack. it could be electrical noise.
what speakers did you want to connect? unpowered 2.0? powered 2.1? powered 5.1?
--
for 2.0 unpowered. you might not be able to power them with the extractor like i listed below for 2.1. worth a try i suppose but i cant guarantee that it will work.
--
if you have a powered 2.1 set you could use a hdmi audio extractor like this one
http/www.ebay.com/itm/HDMI-to-HDMI-Optical-SPDIF-RCA-L-R-Audio-Extractor-Converter-Audio-Splitter-/251468319879 to pull audio from your ps3. you would need a rca (red+white) 2x male connector to 1x 3.5mm stereo connector female which you could plug the green 3.5mm cord into. for connecting to your pc i would just use the back of your computer or headphone jack.
if you want both connected at once.. you could just use a 3.5mm splitter. one Y going to the output of the above device. one Y going to the output of the pc. the single end being female and going to the speakers.
if you are using a 2.1 set you can get off relatively cheap.
i'm guessing since you mentioned you plugged into your monitor that you have a 2.1... (well it could be a 2.0 as well)
---
if you have a powered 5.1
you could get a hdmi audio extractor which has 6 rca ports similar to the above mentioned one but they get expensive and are very hard to find. most of them instead are for optical/coax spdif outputs.
another option: you could have the speakers hooked up to your computer only and have a soundcard which is capable of accepting a spdif optical input signal. you would then run optical from your ps3 to this soundcard and with the pc on have it play the audio input from the ps3. its not cheap and not pretty but it works. the trouble is not many soundcards accept input in this way (which is why i said not cheap)
yet another option: get a speaker set with an optical input. not the cheapest option but would allow you to connect the ps3 up via optical and the pc up via 3.5mm at the same time. i know the z906 has this (but its expensive) i am not aware of other models.. you would have to look it up.
and another: you could output your pc and ps3 via optical and use something like this
http/www.amazon.com/Panlong-Audio-Digital-Decoder-Converter/dp/B00AMC2J1Y
5.1 would not be a cheap option to fix.