Client reports a loud rattling noise is occurring in the attic from the furnace. System cools still. Findings: (1) Turned on FAN ONLY and the rattling would occur. (2) Went up to the attic and found that the blower wheel was loose. (3) Took out the blower housing and inspected the internals. (4) Found the integrity of the blower wheel and the motor's shaft to be lacking. Recommendations: (1) The blower motor and the blower wheel are unstable amd need to be replaced to restore proper operation. (2) The furnace is from 1994 (26 years old). These units tend to last 15-20 years. It would be wise to consider replacement options.