time to rebuild your Clutch master cylinder. I just did that 3 weeks ago. The sound your describing is a metal hitting metal sound. Have a friend of yours push in the clucth for you and feel the end of the Clutch M cylinder. You'll feel the piston hitting the end of the cylinder. The rubber busings around the pistons are probably worn out.

making sense yet?

you can get a clutch master rebuild kit for around 15bucks. Its fairly a simple task.

or you could buy a new CMC for 60-70 dollars.

Good luck

later.