When the CEL is turned on all the time, fuel consumption and performance would be affected.
P0300 - P0304 are misfiring codes and it could be anything from bad spark plug and/or wires to faults with fuel pressure.
2 years is a long time and anything from contaminations to failed components can cause the misfire.
It is not possible to comment on the noise as its source is not clear.
Friday, January 14th, 2011 AT 5:54 PM