I have a 2002 Ford Explorer Sport Trac, the automatic V-6, with just over 90k miles. I have have owned it since new, and I have nothing but praise for it. However, recently I have been noticing a squeal when the engine hits about 1900 rpms, but only in certian conditions.
It mostly happens when I am going up a small hill/incline and the engine hits 1900-ish rpms. It only lasts for a few seconds and is solved by accelerating or decelerating up the hill. It is not a loud or high pitched squeal, but it noticible. It happens whether I am going 35mph on a side road or 75mph on the highway.
Should I take it in for service (if so, what might be the issue), or is it just a sign of old age? I did have a major front accident on an icy New England day with a telephone pole. This was in 2004, and the noise only started in the past year.
Any input would be great 
One more problem I am having that may or may not be related is; when I put the car in reverse from a cold start, the engine ‘pulses’. It creates a similar effect to pumping the brakes. It has been happening for about a month or so, and recently I have noticed it a little when I am ‘D’/forward (automatic transmision), from a cold start. It does not happen as much, or at all if it shift into reverse/‘D’ after driving for a while.
When was the last time you checked the automatic transmission fluid? How about the accessory belt?
The oil and transmission fluid were changed at 90000 miles (2k miles ago). I have no idea about the accessory belt. I beleive the timing belt needs to be changed at 100k miles, and I am going to have that done with the next oil change. It is possible that could be what is cause both/either problem?