38000 miles and engine makes a himming sound when acelerating and winds down when you take foot off gas, no noise when idling. Auto trans, could it be that or fan or engine.

My guess:

You likely change the engine oil and filter on schedule. Most people, however, neglect to change the transmission fluid and filter. Here's some advice on the subject:

https://www.askmehelpdesk.com/cars-t...tml#post552241

If you take good care of the engine and transmission, everything else is relatively minor.