What makes you think they're loose?
There isn't any "no matter what I do" - there is no adjustment for valve springs.
The only things I can think of that will make a spring loose are:
1. you lost a lock, which means that valve and piston are toast
2. the spring is broken, and the valve will fall in any moment
In either case, don't even start it again "just to see if the noise is still there", because it may destroy another piston.
Take off the valve cover, and look for something obviously wrong.
