F50 w/ occasional high pitch tone from rear?

[O5Q45]

I've noticed lately on deceleration a high pitch tone/noise coming from the rear of the car. The tone/noise is not mechanical in nature but as if electrical? This morning on cold start, I always let the car run a minute to a minute and a half or till the tach starts to settle to allow all fluids and systems to do there thing and get where they need to be.. however this morning the high pitch tone was much more noticeable and louder... I had a GM car in high school that did this for years.. only thing I can imagine is the fuel pump? Ideas?