Craftsman Model 917.276903 rattle in undercarriage

Hello,

I have the mower referenced in subject line (Craftsman Model 917.276903) and am experiencing a rattle which sounds like a rod knocking in the undercarriage. When I even slightly put pressure on the cluthc/brake pedal it stops. This does not appear to interfer with the mechanical functioning of the tractor at all but is grating on my nerves. Any suggestions?

Thanks,

RL9144