As I mentioned on your twitter (@NotActuallyJack here), those gaskets will help a lot, something else you can do which will help is get a mic windscreen, as it will act as a low-bias squelch. Another more extensive mod to cut the noise would be to get some thin rubber sheeting and attach it to the flat surfaces exposed on inside of case to help kill how much the sound can reflect around. If that STILL isn't enough, cut a few egg cartons in half and make an isolation screen, ie tape them to backing or side to side and place in front of case to act as brute noise barrier. Egg cartons on inside of hutch etc (case home) will also help as it will again cut down on reflected sound around sides of case from back fan.
Good Luck!

So you mean something like this?

https://www.amazon.co.uk/Electrovision-G132DA-Internal-Microphone-Windshield/dp/B000KFVBH6?ie=UTF8&;*Version*=1&*entries*=0

Yes, exactly.

Okay I've ordered that, for the price I can't really complain, if it even helps a bit it will be worth it!

I can't seem to find a gasket/cover that will fit my 140mm deep silence fan sadly, any idea where's a cheap place (in the UK) to order some of the washers from. You put them on the outside between the screw and the case right?

One extremely obvious but completely serious suggestion: Move the microphone farther away from the computer. Like to the other side of your desk. Even half a metre of extra distance might do wonders.

I'll look for a 140mm for you in a bit, is early morning for me (west coast US). But yeah, the gaskets go on side compression is coming from, so if you screw in from outside they go on that side, if you screw from inside they go between case and fan housing; goal is really just to keep vibrations in fan from becoming vibrations on case. If you buy the washers from a hardware store (they sell baggies of the cheap paper kind that work fine) it really doesn't hurt to have washers on both sides, between head of screw and case and between fan and case.

Quoting: tuubiOne extremely obvious but completely serious suggestion: Move the microphone farther away from the computer. Like to the other side of your desk. Even half a metre of extra distance might do wonders.

My pc sits to the right of my desk, my microphone is on top on the left of my desk, it's as far away as I can make it go.

Another problem is my PSU fan seems to be acting up, getting a fair amount of noise and vibration from it. Have sent an email to the PC maker about it.

Quoting: liamdaweAnother problem is my PSU fan seems to be acting up, getting a fair amount of noise and vibration from it. Have sent an email to the PC maker about it.

I absolutely love my Corsair RM-series PSU. The fan only starts spinning when there's significant power draw, and my measly i7/GTX 960 setup has never actually managed to make it budge. The dust filter under it is always clean. :)

Rubber washers for the case fan help a bit (and they're only a couple of pounds) as other have suggested. Depending on how the PSU is in there, you could add some to that too. Then bigger case fans are usually better in terms of noise.

With the PSU, it might be that your power consumption is too high for it. That's a part that if it's doing weird things, I'd definitely look into replacing. If that burns out, you risk your GPU and CPU as well.

The PSU is being replaced by the system builder, it's not due to power draw as I've used it extensively since last year when I got it (it's the correct power for the system).

Sadly my old silent PSU won't work with the type of case I have, as the power button is hooked up to a circuitboard, and it requires a specific connector that PSU doesn't have :(