A few days ago my motor started rattling,between 2000 and 4000 rpms in first and second gear it does it when reved in neutrel but only when its cold,once it warms up it only does it in drive.The sound is almost like the fan if it was hitting something(ITS NOT)I have'nt experianced any power loss but i have noticed smoke from my valve cover breathers.Could this be a clogged cat/exhaust leak problem or do yall think its in the heads......