i have a new to me 2003 XJ8 with 93K---beautiful lady driven auto. just put on new michelins-----when i am driving in regular drive---at EXACTLY 50mph-there is a sound like a harmonic or the intake on my ducati under full throttle!!----if i hold it there and simultaniously shift to sport---its gone!!---if i slide the gearlever over to 4th--it goes away---if i run from 0 to 90mph right up through the gears----donot hear anything----if i start at 0 and manually shift through 4th---nothing!!---------if i am at 50 and the noise is there and drop to 48mph--gone if i continue on up it will be tottaly gone by 55mph--if i drive in sport mode i have no problem------my mech put sensors on several places including xmission---seems to be coming from rear of tranny and sounds like a bearing.the mech says it is likely nothing to worry about---DRIVE IT!----------my wife says --turn on the radio!!---------my XJR had a similar sound and i always thought it was the SC.-----I am **** !!! i would like to have some pro thoughts------thanks doug 352 634 4685 bkrdoug@yahoo.com

 

I do not remember the speed that the torque converter locks on the XJ8, but it is around 50- I think it might be 52 mph.

 

FIXED!!!!!!!!!!!!!----of the 4 big bolts that hold exhaust to cat. conv., 2 were missing and 2 were loose.-------noise gone. thx doug