My 240 will emit a high pitch howl between 25-30 mph when cold until car warms up--driven about 4-5 miles. Sound does not return until it sits over nite again. Have owned car for 3 months and this is the first it has done this. Now, the outside over nite temps have been in high 40's/low 50's and not sure if part of mix. While making this noise, I have put car in neutral and still there. I have tried to turn steering while noise there and does not change pitch or stop. Any ideas?? I'm guessing bearing, but from where?