In one of the infrequently used bedrooms in my home, the carpet has started to "bubble" in the center of the room. A long section has lifted up into a small hill and I'm wondering if there is an inexpensive way to repair this problem. Is there something I can easily do to flatten it out? I've called about having it stretched, but found that is quite pricey. I'd like that to be a last resort. Any suggestions or information would be great appreciated!