Hi and thanks for your interest - I am not sure if its the cat, I had a slight cat rattle on my old e38 m62tu and though similar its not the same since this noise is cyclic in that it increases in frequency along with the RPM. I must point out that the noise is so faint that if the radio is on even softly or the interior fan is on low speed the noise is not audible - it comes in at around 1500rpm and is gone by 3000rpm.

I spent New Years with my folks and returned home this evening after a very fast trip - I figured if it was gone blow, then ......... but after 250 miles and average speed of 100mph with the odd 130 or so the noise appears to be no worse.

I guess i will have to get out my stethoscope doo-dad and try to isolate the problem. I am also considering draining the oil and sending it for analasis.

There is also the possibilty of just trading it for something else.

About those engines - I found 2 candidates, a 650i and a e70 4.8i both wrecks (rear damage) I would still like to know if the 4.8 will run off the 4.4 ecu?

Thanks again everybody

Andrew