Whistle coming from inside 306

[Pipsqueakaboo]

Hi guys!! I'm new here and this is my first car so I'm still getting the hang of things. 

My little pug. He's old now (1999) and I know it's gettin on and things will be breaking down. I bought it for £500 off a friend who knew nothing about cars, therefore did nothing to really look after it. 

I had the MOT done in December and had, ALOT, of stuff done. 

New tyres, new cat, brake load sensing valve had gone, drop link something had seized up. So I paid a lot for it to be repaired. 

But now I have noticed a lot of water in the passenger footwell. I put kseal through the system and it cleared up. But the water is back and it's more like a puddle now. 

I can't be sure weather it's because of heavy rain (we had a lot of rain both times before the water appeared) or if there is a leak. 

And also. When I start up my engine. Recently it's started whistling/screeching. And it's really high pitched. It sounds like it's coming from the dash. It's deafening. But then it stops. I don't know what is causing it. Sometimes it doesn't do it. And sometimes it does. 

Sorry for the really long post btw!!