My floors (2nd) floor)are squeaking under the carpet, I'd rather not pull up the carpet to fix. What can I do. It's very annoying

To really fix it you need to pull back the carpet and pad... and from there, the right solution would depend on what material floor you have. If you have plywood, driving a few extra screws into it should do the trick.

Then you'd only need to have someone come in and restretch it.

You can, though, try to Rube Goldberg it.

Where the floor squeaks the most, drive a fat finishing nail into it at an angle.
Yep, right through the carpet.

You'll very carefully separate the carpet with your fingers and starting the nail right into the backing of the carpet, to be sure you're not driving carpet itself down through... then follow your nail head with a nail punch - to get it's head down to the surface of the floor.

Of the few times I've tried this, it's worked about half the time.

NOTE: Done right, this will be completely un-noticeable and will not damage the carpet in any way. Done wrong will damage the carpet.

Only try this if you completely understand what I'm trying to get at with it.

Let me know if I can clarify further.