Andy Gside

After the 4 month wait my carbon bonnet is finally here and on 👌 next week getting ppf wrapped to keep it protected 

Electronic sound is definitely the throttle body. 
This hiss, I think mine does this, not sure what it is, whether its the AC, or the vacuum system draining. 

Damn dude you made a really nice job of this! Looks proper tidy  cant wait to see where else you go with this!
Even the interior colour mods make a world of difference, I'm hoping I get some time soon to do something similar to mine. Not a fan of the stock silver plastic look.

After the 4 month wait my carbon bonnet is finally here and on 👌 next week getting ppf wrapped to keep it protected 

Just got my self some not ran them yet waiting till after winter

Someone has been busy. Not one part of your car left unfettled. Some inspiration of what can be done. The wood floor in the boot is bonkers. Ha ha. 

Managed to get a bargin by from a fellow member, full whiteline suspension kit, and got the 15mm tein lowering springs brand new from partbox 

Back in 2017 I had my car modified at Abbey, I had an ACE CS400 manifold installed, alongside a Cobra HFC. Performance is great, torque dip eliminated. However I was never that happy with the sound. It was okay-ish with the rest of the exhaust stock but I kept looking for options to make it sound better.
Last year during lockdown I purchased a Q300 catback, which is meant to be one of the quieter systems, but I still found it a bit loud and droney at about 2.5K RPM. I got rid after three months. I then went to just a Remus backbox, still with the ACE and the Cobra HFC. Much more bearable than the Q300. But was still getting a little bit of annoying rasp sometimes at low revs.
So last month, I decided to see if removing the HFC made a difference. I swapped it out and went back to the OEM front pipe, which has a resonator. That has got rid of the rasp, and I haven't really noticed any loss of performance or efficiency. That said, I'm not a track driver, and probably don't drive as hard as most, so I might have lost a tad of top end power but not noticed. But I am at least happy with the sound now. So the exhaust system now goes ACE manifold > OEM front pipe > OEM midpipe > Remus backbox.
All that is a long way of saying that in my experience, I've found that the system sounds better with the OEM front pipe, and I've haven't really noticed if going back to it reduced power. If you're getting a decat manifold, just be aware that a high flow cat might make the system noisy if you have anything other than an OEM catback. Whether that bothers you or not is up to you. 
As for MOT compliance....I think the general consensus is that with a decatted manifold, and the second cat in the front pipe replaced with a HFC, you might be at risk of not passing emissions - at the very least you will have to make sure it's tested with the exhaust piping hot to make sure it passes. Mine has never failed the MOT since it's been running with just the Cobra HFC as the only cat...however that's because I've made sure to always take it back to Abbey for the MOT, who will make sure to test it when it's thoroughly warmed up. 

Two thoughts on this
A.) The engine bay isn't water tight and everything is designed to get wet
B.) My car looks like a steam train when the wraps get wet and they puff.
Personally I put something (usually a flattened piece of cardboard) under the bonnet when the car is outside and parked, and this is more to keep excess moisture off the wraps / air intake. I also have some rain guards, but TBH i found them a PITA to take off when I wanted to drive the car, and I always removed them when driving regardless of weather.
Another factor on the rain-guards was they are excellent funnels for melted ice water when snow rests on them.
My take, I don't worry about, if things break then it's a great excuse to upgrade them.

I'm perhaps the best or worst person to answer this haha.
When i first got my car I originally fitted a vented Carbon bonnet and I dailied the car for about 18 months through all weather. During that time a bit of rain would just meant that the belt would slip for a few seconds when starting the car, no big deal really as i'd give it a rev and it would grab and be fine no problems!
 
But then after I took my car off the road for 5 odd months, did a load of work on it and eventually started driving it again suddenly one of my idle pulleys on the belt system had a bearing failure! (the one directly under the intake) it's hard to say whether this was caused by the 18 odd months of rain etc potentially getting on to the belt & pulley but I've not done anything about it since replacing the pulley, then again I don't daily the car anymore.
 
That's my experience atleast