Toilet makes noise like a foghorn, like it has air in the pipes, but when you touch the float ball it stops. What could the problem be?

Which type of valve do you have in the tioilet?

Answer Harolds question, we both might be able to help. I'm getting this moved to plumbing so the plumbers can give use thebenefit of their experience. Sounds like the diaphram in the ballcock is not closing all the way and is vibrating. Touching the float is just enough to get the valve closed and the vibrating stopped. I don't fix most ballcocks because they aren't worth the ffort most of the time. For $10 I can put in a 4ooa replacement ballcock and be done with it, plus labor.