I'm really sorry, but that sounds like the drive is broken. The churning noise would indicate that either internals have been knocked out of place, or possibly even snapped off as the drive isn't built to handle more than one disk.
If the console was less than a year old, you would have been entitled to a free replacement, but as you've opened it, that's now invalid. You could contact Sony and pay £130 for a replacement if they offer it, or you could try taking it to a place like GameStation and seeing if they can repair it for you.
The contact details for Sony Customer Support can be found here.