If the problem is occurring on one jack try using a known-working corded phone on that jack. If that fixes it than you may have a problem with your original phone.

If the problem is occurring on all jacks make sure you remove any equipment such as (fax machines, cordless telephones, answering machines, etc.). Plug in a known-static-free telephone into one jack and check it. If the static is gone than it was probably a peice of your equipment.